reverted:
--- b/core/modules/block/tests/src/Functional/BlockTest.php
+++ a/core/modules/block/tests/src/Functional/BlockTest.php
@@ -244,11 +244,6 @@
     $xpath = $this->assertSession()->buildXPathQuery('//div[@id=:id]/*', [':id' => 'block-' . str_replace('_', '-', strtolower($block['id']))]);
     $this->assertSession()->elementNotExists('xpath', $xpath);
 
-    // Test error when not including forward slash.
-    $this->drupalGet('admin/structure/block/manage/' . $block['id']);
-    $this->submitForm(['visibility[request_path][pages]' => 'user/login'], 'Save block');
-    $this->assertSession()->pageTextContains('Paths require a leading forward slash when used with the Pages setting.');
-
     // Test deleting the block from the edit form.
     $this->drupalGet('admin/structure/block/manage/' . $block['id']);
     $this->clickLink('Remove block');
reverted:
--- b/core/modules/system/src/Plugin/Condition/RequestPath.php
+++ a/core/modules/system/src/Plugin/Condition/RequestPath.php
@@ -112,22 +112,6 @@
     return parent::buildConfigurationForm($form, $form_state);
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
-    $paths = explode("\r\n", $form_state->getValue('pages'));
-    foreach ($paths as $path) {
-      if (empty($path) || $path === '<front>' || strpos($path, '/') === 0) {
-        continue;
-      }
-      else {
-        $form_state->setErrorByName('pages', $this->t('Paths require a leading forward slash when used with the Pages setting.'));
-        return;
-      }
-    }
-  }
-
   /**
    * {@inheritdoc}
    */
only in patch2:
unchanged:
--- a/core/modules/block/src/Controller/BlockLibraryController.php
+++ b/core/modules/block/src/Controller/BlockLibraryController.php
@@ -104,6 +104,14 @@ public function listBlocks(Request $request, $theme) {
     $region = $request->query->get('region');
     $weight = $request->query->get('weight');
 
+    // Adds to the "Add custom block" action url route parameters, to provide
+    // correct region setting after creation.
+    $add_action_url = $build['local_actions']['block_content_add_action']['#link']['url'] ?? NULL;
+    if ($add_action_url instanceof Url) {
+      $add_action_url->setRouteParameter('region', $region);
+      $build['local_actions']['block_content_add_action']['#link']['url'] = $add_action_url;
+    }
+
     // Only add blocks which work without any available context.
     $definitions = $this->blockManager->getFilteredDefinitions('block_ui', $this->contextRepository->getAvailableContexts(), [
       'theme' => $theme,
only in patch2:
unchanged:
--- a/core/modules/block_content/src/BlockContentForm.php
+++ b/core/modules/block_content/src/BlockContentForm.php
@@ -73,6 +73,7 @@ public function save(array $form, FormStateInterface $form_state) {
           [
             'plugin_id' => 'block_content:' . $block->uuid(),
             'theme' => $theme,
+            'region' => $this->getRequest()->query->get('region'),
           ]
         );
       }
only in patch2:
unchanged:
--- a/core/modules/block_content/src/Plugin/Menu/LocalAction/BlockContentAddLocalAction.php
+++ b/core/modules/block_content/src/Plugin/Menu/LocalAction/BlockContentAddLocalAction.php
@@ -20,6 +20,12 @@ public function getOptions(RouteMatchInterface $route_match) {
     if ($theme = $route_match->getParameter('theme')) {
       $options['query']['theme'] = $theme;
     }
+
+    // If the current request has a region query parameter.
+    if ($region = \Drupal::request()->query->get('region')) {
+      $options['query']['region'] = $region;
+    }
+
     // Adds a destination on custom block listing.
     if ($route_match->getRouteName() == 'entity.block_content.collection') {
       $options['query']['destination'] = Url::fromRoute('<current>')->toString();
only in patch2:
unchanged:
--- a/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
@@ -120,4 +120,23 @@ public function testListing() {
     $this->assertSession()->pageTextNotContains('Non-reusable block');
   }
 
+  /**
+   * Tests that region value is retained when we create new block.
+   */
+  public function testBlockRegionPlacement() {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'translate configuration',
+    ]));
+    $this->drupalGet("admin/structure/block/library/stark", ['query' => ['region' => 'help']]);
+
+    $this->clickLink('Add custom block');
+    $this->assertSession()->statusCodeEquals(200);
+    $edit = [
+      'info[0][value]' => $this->randomString(),
+    ];
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->fieldValueEquals('region', 'help');
+  }
+
 }