diff --git a/core/lib/Drupal/Component/Datetime/DateTimePlus.php b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
index 2134ffb..0386faf 100644
--- a/core/lib/Drupal/Component/Datetime/DateTimePlus.php
+++ b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
@@ -30,6 +30,18 @@
  * The parent class would convert that value to '2010-11-30' and report
  * a warning but not an error. This extension treats that as an error.
  *
+ * This class adds a test for the creation of a date using a string
+ * that includes a timezone offset or abbreviation because anything
+ * other than a complete timezone name results in ambiguity and
+ * inaccuracy since there are many timezones that use the same
+ * abbreviation and offset. Without a complete timezone name we
+ * can't modify or compare the date correctly. In addition, a
+ * date created this way has a timezone name that can't be used
+ * to create a valid timezone object. We can't guess the real
+ * timezone from those values, and we can't tell what was intended
+ * if that offset does not match the timezone that was input.
+ * @see http://derickrethans.nl/gmt-being-tricky.html
+ *
  * As with the base class, a date object may be created even if it has
  * errors. It has an errors array attached to it that explains what the
  * errors are. This is less disruptive than allowing datetime exceptions
@@ -127,7 +139,7 @@ class DateTimePlus extends \DateTime {
    *   date will be created using the createFromFormat() method.
    *   Defaults to NULL.
    *   @see http://us3.php.net/manual/en/datetime.createfromformat.php
-   * @params array $settings
+   * @param array $settings
    *   - boolean $validate_format
    *     The format used in createFromFormat() allows slightly different
    *     values than format(). If we use an input format that works in
@@ -197,6 +209,9 @@ public function __construct($time = 'now', $timezone = NULL, $format = NULL, $se
       $this->constructFallback();
     }
 
+    // Final validity check.
+    $this->checkValidity();
+
     // Clean up the error messages.
     $this->getErrors();
     $this->errors = array_unique($this->errors);
@@ -447,6 +462,63 @@ public function constructFallback() {
   }
 
   /**
+   * Final validation tests
+   *
+   * If a date was created from a string with a timezone offset or
+   * timezone abbreviation, like +10:00 or 'EST', the input timezone
+   * will be ignored and the value created may be incorrect and won't
+   * be modified correctly across daylight savings time. It also
+   * creates a date that has a timezone name (+10:00, or 'EST'),
+   * that is invalid input for creating another timezone object.
+   * This can only happen if a timezone offset or abbreviation is
+   * appended to the input time string because it's impossible to
+   * create a timezone object from these values.
+   *
+   * We first check to see if the provided abbreviation or offset
+   * seems to match the provided timezone name. If so, the timezone
+   * name is updated. If not, an error is thrown.
+   */
+  public function checkValidity() {
+
+    // If we already have errors, these tests might not work.
+    if (!empty($this->errors)) {
+      return;
+    }
+
+    // See if the created timezone is a timezone abbreviation.
+    $created_timezone = $this->getTimezone()->getName();
+    if (strlen($created_timezone) <= 4 && $created_timezone != 'UTC') {
+      $match = FALSE;
+      $abbr = strtolower($created_timezone);
+      $timezone_abbreviations = \DateTimeZone::listAbbreviations();
+      foreach ($timezone_abbreviations[$abbr] as $abbreviation) {
+        if ($abbreviation['timezone_id'] == $this->input_timezone_adjusted->getName()) {
+          $match = TRUE;
+          break;
+        }
+      }
+      if ($match) {
+        $this->setTimezone($this->input_timezone_adjusted);
+      }
+      else {
+        $this->errors[] = 'The input time includes a timezone abbreviation that is inconsistent with the timezone name.';
+      }
+    }
+
+    // Otherwise see if the created timezone is an offset.
+    elseif (!preg_match('/[a-zA-Z_]/', $created_timezone)) {
+      $string_offset = $this->getOffset();
+      $comp = new \DateTime($this->format('Y-m-d H:i:s'), $this->input_timezone_adjusted);
+      if ($this->getOffset() == $comp->getOffset()) {
+        $this->setTimezone($this->input_timezone_adjusted);
+      }
+      else {
+        $this->errors[] = 'The input time includes a timezone offset that is inconsistent with the timezone name.';
+      }
+    }
+  }
+
+  /**
    * Examine getLastErrors() and see what errors to report.
    *
    * We're interested in two kinds of errors: anything that DateTime
@@ -634,7 +706,7 @@ function canUseIntl() {
    * @param string $format
    *   A format string using either PHP's date() or the
    *   IntlDateFormatter() format.
-   * @params array $settings
+   * @param array $settings
    *   - string $format_string_type
    *     Which pattern is used by the format string. When using the
    *     Intl formatter, the format string must use the Intl pattern,
diff --git a/core/lib/Drupal/Core/Datetime/DrupalDateTime.php b/core/lib/Drupal/Core/Datetime/DrupalDateTime.php
index 9378406..d917c3e 100644
--- a/core/lib/Drupal/Core/Datetime/DrupalDateTime.php
+++ b/core/lib/Drupal/Core/Datetime/DrupalDateTime.php
@@ -36,7 +36,7 @@ class DrupalDateTime extends DateTimePlus {
    *   date will be created using the createFromFormat() method.
    *   Defaults to NULL.
    *   @see http://us3.php.net/manual/en/datetime.createfromformat.php
-   * @params array $settings
+   * @param array $settings
    *   - boolean $validate_format
    *     The format used in createFromFormat() allows slightly different
    *     values than format(). If we use an input format that works in
@@ -75,6 +75,18 @@ public function __construct($time = 'now', $timezone = NULL, $format = NULL, $se
   }
 
   /**
+   * Override basic component timezone handling to use Drupal's
+   * knowledge of the preferred user timezone.
+   */
+  public function prepareTimezone($timezone) {
+    $user_timezone = drupal_get_user_timezone();
+    if (empty($timezone) && !empty($user_timezone)) {
+      $timezone = $user_timezone;
+    }
+    parent::prepareTimezone($timezone);
+  }
+
+  /**
    * Format the date for display.
    *
    * Use the IntlDateFormatter to display the format, if available.
@@ -86,7 +98,7 @@ public function __construct($time = 'now', $timezone = NULL, $format = NULL, $se
    * @param string $format
    *   A format string using either date() or IntlDateFormatter()
    *   format.
-   * @params array $settings
+   * @param array $settings
    *   - string $format_string_type
    *     Which pattern is used by the format string. When using the
    *     Intl formatter, the format string must use the Intl pattern,
diff --git a/core/modules/system/lib/Drupal/system/Tests/Datetime/DateTimePlusTest.php b/core/modules/system/lib/Drupal/system/Tests/Datetime/DateTimePlusTest.php
index b268914..4eba36d 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Datetime/DateTimePlusTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Datetime/DateTimePlusTest.php
@@ -73,6 +73,23 @@ public function testDateStrings() {
     $value = $date->format('c');
     $expected = '2009-06-07T00:00:00-05:00';
     $this->assertEqual($expected, $value, "Test new DateTimePlus($input, $timezone): should be $expected, found $value.");
+
+    // Create date object from date string.
+    $input = '2009-03-07 10:30';
+    $timezone = 'Australia/Canberra';
+    $date = new DateTimePlus($input, $timezone);
+    $value = $date->format('c');
+    $expected = '2009-03-07T10:30:00+11:00';
+    $this->assertEqual($expected, $value, "Test new DateTimePlus($input, $timezone): should be $expected, found $value.");
+
+    // Same during daylight savings time.
+    $input = '2009-06-07 10:30';
+    $timezone = 'Australia/Canberra';
+    $date = new DateTimePlus($input, $timezone);
+    $value = $date->format('c');
+    $expected = '2009-06-07T10:30:00+10:00';
+    $this->assertEqual($expected, $value, "Test new DateTimePlus($input, $timezone): should be $expected, found $value.");
+
   }
 
   /**
@@ -96,6 +113,23 @@ function testDateArrays() {
     $expected = '2010-02-28T10:00:00-06:00';
     $this->assertEqual($expected, $value, "Test new DateTimePlus(array('year' => 2010, 'month' => 2, 'day' => 28, 'hour' => 10), $timezone): should be $expected, found $value.");
 
+    // Create date object from date array, date only.
+    $input = array('year' => 2010, 'month' => 2, 'day' => 28);
+    $timezone = 'Europe/Berlin';
+    $date = new DateTimePlus($input, $timezone);
+    $value = $date->format('c');
+    $expected = '2010-02-28T00:00:00+01:00';
+    $this->assertEqual($expected, $value, "Test new DateTimePlus(array('year' => 2010, 'month' => 2, 'day' => 28), $timezone): should be $expected, found $value.");
+
+    // Create date object from date array with hour.
+    $input = array('year' => 2010, 'month' => 2, 'day' => 28, 'hour' => 10);
+    $timezone = 'Europe/Berlin';
+    $date = new DateTimePlus($input, $timezone);
+    $value = $date->format('c');
+    $expected = '2010-02-28T10:00:00+01:00';
+    $this->assertEqual($expected, $value, "Test new DateTimePlus(array('year' => 2010, 'month' => 2, 'day' => 28, 'hour' => 10), $timezone): should be $expected, found $value.");
+
+
   }
 
   /**
@@ -226,6 +260,23 @@ function testTimezoneConversion() {
     $value = $date->getOffset();
     $this->assertEqual($expected, $value, "The current offset should be $expected, found $value.");
 
+    // Convert the local time to UTC using string input.
+    $input = '1969-12-31 16:00:00';
+    $timezone = 'Europe/Warsaw';
+    $date = new DateTimePlus($input, $timezone);
+    $offset = $date->getOffset();
+    $value = $date->format('c');
+    $expected = '1969-12-31T16:00:00+01:00';
+    $this->assertEqual($expected, $value, "Test new DateTimePlus('$input', '$timezone'):  should be $expected, found $value.");
+
+    $expected = 'Europe/Warsaw';
+    $value = $date->getTimeZone()->getName();
+    $this->assertEqual($expected, $value, "The current timezone should be $expected, found $value.");
+    $expected = '+3600';
+    $value = $date->getOffset();
+    $this->assertEqual($expected, $value, "The current offset should be $expected, found $value.");
+
+
   }
 
   /**
@@ -277,7 +328,7 @@ function testDateFormat() {
   function testInvalidDates() {
 
     // Test for invalid month names when we are using a short version
-    // of the month
+    // of the month.
     $input = '23 abc 2012';
     $timezone = NULL;
     $format = 'd M Y';
@@ -340,6 +391,42 @@ function testInvalidDates() {
   }
 
   /**
+   * Test that DrupalDateTime can detect the right timezone to use.
+   * When specified or not.
+   */
+  public function testDateTimezone() {
+    global $user;
+
+    $date_string = '2007-01-31 21:00:00';
+
+    // Detect the system timezone.
+    $system_timezone = date_default_timezone_get();
+
+    // Create a date object with an unspecified timezone, which should
+    // end up using the system timezone.
+    $date = new DateTimePlus($date_string);
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == $system_timezone, 'DateTimePlus uses the system timezone when there is no site timezone.');
+
+    // Create a date object with a specified timezone name.
+    $date = new DateTimePlus($date_string, 'America/Yellowknife');
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == 'America/Yellowknife', 'DateTimePlus uses the specified timezone if provided.');
+
+    // Create a date object with a timezone object.
+    $date = new DateTimePlus($date_string, new \DateTimeZone('Australia/Canberra'));
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == 'Australia/Canberra', 'DateTimePlus uses the specified timezone if provided.');
+
+    // Create a date object with another date object.
+    $new_date = new DateTimePlus('now', 'Pacific/Midway');
+    $date = new DateTimePlus($new_date);
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == 'Pacific/Midway', 'DateTimePlus uses the specified timezone if provided.');
+
+  }
+
+  /**
    * Tear down after tests.
    */
   public function tearDown() {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php b/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php
new file mode 100644
index 0000000..ea10896
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php
@@ -0,0 +1,110 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\system\Tests\Datetime\DateTimePlusTest.
+ */
+
+namespace Drupal\system\Tests\Datetime;
+
+use Drupal\simpletest\WebTestBase;
+use Drupal\Core\Datetime\DrupalDateTime;
+
+class DrupalDateTimeTest extends WebTestBase {
+
+  /**
+   * Test information.
+   */
+  public static function getInfo() {
+    return array(
+      'name' => 'DrupalDateTime',
+      'description' => 'Test DrupalDateTime functionality.',
+      'group' => 'Datetime',
+    );
+  }
+
+  /**
+   * Set up required modules.
+   */
+  public static $modules = array();
+
+  /**
+   * Test setup.
+   */
+  public function setUp() {
+    parent::setUp();
+
+  }
+
+  /**
+   * Test that DrupalDateTime can detect the right timezone to use.
+   * Test with a variety of less commonly used timezone names to
+   * help ensure that the system timezone will be different than the
+   * stated timezones.
+   */
+  public function testDateTimezone() {
+    global $user;
+
+    $date_string = '2007-01-31 21:00:00';
+
+    // Make sure no site timezone has been set.
+    variable_set('date_default_timezone', NULL);
+    variable_set('configurable_timezones', 0);
+
+    // Detect the system timezone.
+    $system_timezone = date_default_timezone_get();
+
+    // Create a date object with an unspecified timezone, which should
+    // end up using the system timezone.
+    $date = new DrupalDateTime($date_string);
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == $system_timezone, 'DrupalDateTime uses the system timezone when there is no site timezone.');
+
+    // Create a date object with a specified timezone.
+    $date = new DrupalDateTime($date_string, 'America/Yellowknife');
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == 'America/Yellowknife', 'DrupalDateTime uses the specified timezone if provided.');
+
+    // Set a site timezone.
+    variable_set('date_default_timezone', 'Europe/Warsaw');
+
+    // Create a date object with an unspecified timezone, which should
+    // end up using the site timezone.
+    $date = new DrupalDateTime($date_string);
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == 'Europe/Warsaw', 'DrupalDateTime uses the site timezone if provided.');
+
+    // Create user.
+    variable_set('configurable_timezones', 1);
+    $test_user = $this->drupalCreateUser(array());
+    $this->drupalLogin($test_user);
+
+    // Set up the user with a different timezone than the site.
+    $edit = array('mail' => $test_user->mail, 'timezone' => 'Asia/Manila');
+    $this->drupalPost('user/' . $test_user->uid . '/edit', $edit, t('Save'));
+
+    // Disable session saving as we are about to modify the global $user.
+    drupal_save_session(FALSE);
+    // Save the original user and then replace it with the test user.
+    $real_user = $user;
+    $user = user_load($test_user->uid, TRUE);
+
+    // Simulate a Drupal bootstrap with the logged-in user.
+    date_default_timezone_set(drupal_get_user_timezone());
+
+    // Create a date object with an unspecified timezone, which should
+    // end up using the user timezone.
+
+    $date = new DrupalDateTime($date_string);
+    $timezone = $date->getTimezone()->getName();
+    $this->assertTrue($timezone == 'Asia/Manila', 'DrupalDateTime uses the user timezone, if configurable timezones are used and it is set.');
+
+    // Restore the original user, and enable session saving.
+    $user = $real_user;
+    // Restore default time zone.
+    date_default_timezone_set(drupal_get_user_timezone());
+    drupal_save_session(TRUE);
+
+
+  }
+}