diff -u b/core/modules/block/src/Controller/BlockLibraryController.php b/core/modules/block/src/Controller/BlockLibraryController.php
--- b/core/modules/block/src/Controller/BlockLibraryController.php
+++ b/core/modules/block/src/Controller/BlockLibraryController.php
@@ -104,8 +104,7 @@
     $region = $request->query->get('region');
     $weight = $request->query->get('weight');
 
-    // Add url route parameters to provide correct region setting
-    // after creation.
+    // Add 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);
diff -u b/core/modules/block_content/src/Plugin/Menu/LocalAction/BlockContentAddLocalAction.php b/core/modules/block_content/src/Plugin/Menu/LocalAction/BlockContentAddLocalAction.php
--- b/core/modules/block_content/src/Plugin/Menu/LocalAction/BlockContentAddLocalAction.php
+++ b/core/modules/block_content/src/Plugin/Menu/LocalAction/BlockContentAddLocalAction.php
@@ -21,7 +21,7 @@
       $options['query']['theme'] = $theme;
     }
 
-    // If the current request has a region query parameter.
+    // If the current request has a region, append it to the query string.
     if ($region = $this->request->query->get('region')) {
       $options['query']['region'] = $region;
     }
diff -u b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
--- b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
@@ -70,7 +70,7 @@
   }
 
   /**
-   * Tests that region value is retained when we create new block.
+   * Tests the region value when a new block is saved.
    */
   public function testBlockRegionPlacement() {
     $this->drupalLogin($this->drupalCreateUser($this->permissions));
@@ -79,7 +79,7 @@
     $this->clickLink('Add content block');
     $this->assertSession()->statusCodeEquals(200);
     $edit = [
-      'info[0][value]' => $this->randomString(),
+      'info[0][value]' => 'foo',
     ];
     $this->submitForm($edit, 'Save');
     $this->assertSession()->fieldValueEquals('region', 'help');