diff -u b/src/Plugin/Field/FieldWidget/InlineParagraphsWidget.php b/src/Plugin/Field/FieldWidget/InlineParagraphsWidget.php
--- b/src/Plugin/Field/FieldWidget/InlineParagraphsWidget.php
+++ b/src/Plugin/Field/FieldWidget/InlineParagraphsWidget.php
@@ -1093,7 +1093,7 @@
     $paragraph[] = [
       'entity' => $field_state['paragraphs'][$delta]['entity']->createDuplicate(),
       'display' => $field_state['paragraphs'][$delta]['display'],
-      'mode' => 'closed'
+      'mode' => 'edit'
     ];
     array_splice($field_state['paragraphs'], $delta + 1, 0, $paragraph);
 
diff -u b/src/Tests/ParagraphsWidgetButtonsTest.php b/src/Tests/ParagraphsWidgetButtonsTest.php
--- b/src/Tests/ParagraphsWidgetButtonsTest.php
+++ b/src/Tests/ParagraphsWidgetButtonsTest.php
@@ -137,7 +137,6 @@
     $this->drupalPostAjaxForm(NULL, [], 'field_paragraphs_0_duplicate');
     $this->drupalPostAjaxForm(NULL, [], 'field_paragraphs_0_edit');
     $this->assertFieldByName('field_paragraphs[0][subform][field_text][0][value]', $text);
-    $this->drupalPostAjaxForm(NULL, [], 'field_paragraphs_1_edit');
     $this->assertFieldByName('field_paragraphs[1][subform][field_text][0][value]', $text);
 
     // Save and check if both paragraphs are present.
@@ -146,6 +145,66 @@
   }
 
   /**
+   * Tests duplicate paragraph feature with nested paragraphs.
+   */
+  public function testDuplicateButtonWithNesting(){
+    $this->addParagraphedContentType('paragraphed_test', 'field_paragraphs');
+
+    $this->loginAsAdmin(['create paragraphed_test content', 'edit any paragraphed_test content']);
+    // Add nested Paragraph type.
+    $nested_paragraph_type = 'nested_paragraph';
+    $this->addParagraphsType($nested_paragraph_type);
+    // Add text Paragraph type
+    $paragraph_type = 'text';
+    $this->addParagraphsType($paragraph_type);
+
+    // Add a text field to the text_paragraph type.
+    static::fieldUIAddNewField('admin/structure/paragraphs_type/' . $paragraph_type, 'text', 'Text', 'text_long', [], []);
+
+    // Add a ERR paragraph field to the nested_paragraph type.
+    static::fieldUIAddNewField('admin/structure/paragraphs_type/' . $nested_paragraph_type, 'nested', 'Nested', 'field_ui:entity_reference_revisions:paragraph', [
+      'settings[target_type]' => 'paragraph',
+      'cardinality' => '-1',
+    ], []);
+    $this->drupalPostAjaxForm('node/add/paragraphed_test', [], 'field_paragraphs_nested_paragraph_add_more');
+
+    // Create a node with a Paragraph.
+    $edit = [
+      'title[0][value]' => 'paragraphs_mode_test',
+    ];
+    $this->drupalPostForm(NULL, $edit, t('Save and publish'));
+    $node = $this->drupalGetNodeByTitle('paragraphs_mode_test');
+
+    // Add a text field to nested paragraph
+    $text = 'recognizable_text';
+    $this->drupalPostAjaxForm('node/' . $node->id() . '/edit', [], 'field_paragraphs_0_subform_field_nested_text_add_more');
+    $edit = [
+      'field_paragraphs[0][subform][field_nested][0][subform][field_text][0][value]' => $text,
+    ];
+    $this->drupalPostForm(NULL, $edit, 'Save and keep published');
+
+    // Switch mode to closed
+    $this->setParagraphsWidgetMode('paragraphed_test', 'field_paragraphs', 'closed');
+    $this->drupalGet('node/' . $node->id() . '/edit');
+
+    // Click "Duplicate" button.
+    $this->drupalPostAjaxForm(NULL, [], 'field_paragraphs_0_duplicate');
+    $this->drupalPostAjaxForm(NULL, [], 'field_paragraphs_0_edit');
+    $this->assertFieldByName('field_paragraphs[0][subform][field_nested][0][subform][field_text][0][value]', $text);
+
+    // Change the text paragraph value of duplicated nested paragraph
+    $second_paragraph_text = 'duplicated_text';
+    $edit = [
+      'field_paragraphs[1][subform][field_nested][0][subform][field_text][0][value]' => $second_paragraph_text,
+    ];
+
+    // Save and check if the changed text paragraph value of the duplicated
+    // paragraph is not the same as in the original paragraph
+    $this->drupalPostForm(NULL, $edit, t('Save and keep published'));
+    $this->assertUniqueText($text);
+  }
+
+  /**
    * Sets the Paragraphs widget display mode.
    *
    * @param string $content_type
only in patch2:
unchanged:
--- a/src/Tests/ParagraphsTestBase.php
+++ b/src/Tests/ParagraphsTestBase.php
@@ -129,9 +129,9 @@ abstract class ParagraphsTestBase extends WebTestBase {
       'field_name' => $paragraphs_field_name,
       'entity_type' => $entity_type,
       'type' => 'entity_reference_revisions',
+      'cardinality' => '-1',
       'settings' => [
         'target_type' => 'paragraph',
-        'cardinality' => '-1',
       ],
     ]);
     $field_storage->save();