MAGETWO-43285: If you change page layout on grid, then the node of this page will be removed from hierarchy and Custom Theme will be changed to "Magento Blank"

Author: Bohdan Korablov

app/code/Magento/Cms/Block/Adminhtml/Page/Edit/Tab/Design.php

@@ -156,10 +156,10 @@ protected function _prepareForm()
         );
 
         $designFieldset->addField(
-            'custom_page_layout',
+            'custom_root_template',
             'select',
             [
-                'name' => 'custom_page_layout',
+                'name' => 'custom_root_template',
                 'label' => __('Custom Layout'),
                 'values' => $this->pageLayoutBuilder->getPageLayoutsConfig()->toOptionArray(true),
                 'disabled' => $isElementDisabled

app/code/Magento/Cms/Model/Page/Source/Theme.php

@@ -35,6 +35,7 @@ public function __construct(ListInterface $themeList)
      */
     public function toOptionArray()
     {
-        return $this->themeList->getLabels();
+        $options[] = ['label' => 'Default', 'value' => ''];
+        return array_merge($options, $this->themeList->getLabels());
     }
 }

app/code/Magento/Cms/Test/Unit/Model/Page/Source/ThemeFilterTest.php

@@ -23,13 +23,18 @@ public function getOptionsDataProvider()
         return [
             [
                 [],
-                [['label' => '', 'value' => '']],
+                [
+                    ['label' => '', 'value' => ''],
+                    ['label' => 'Default', 'value' => ''],
+                ],
             ],
             [
                 [['label' => 'testValue', 'value' => 'testStatus']],
-                [['label' => '', 'value' => ''], ['label' => 'testValue', 'value' => 'testStatus']],
+                [
+                    ['label' => '', 'value' => ''],
+                    ['label' => 'Default', 'value' => ''],
+                    ['label' => 'testValue', 'value' => 'testStatus']],
             ],
-
         ];
     }
 }