MC-39953: After changing the layout the theme doesn't apply

Author: OlgaVasyltsun

app/code/Magento/Cms/Controller/Adminhtml/Page/InlineEdit.php

@@ -83,9 +83,9 @@ public function execute()
             /** @var \Magento\Cms\Model\Page $page */
             $page = $this->pageRepository->getById($pageId);
             try {
-                $pageData = $this->filterPost($postItems[$pageId]);
-                $this->validatePost($pageData, $page, $error, $messages);
                 $extendedPageData = $page->getData();
+                $pageData = $this->filterPostWithoutDate($postItems[$pageId], $extendedPageData);
+                $this->validatePost($pageData, $page, $error, $messages);
                 $this->setCmsPageData($page, $extendedPageData, $pageData);
                 $this->pageRepository->save($page);
             } catch (\Magento\Framework\Exception\LocalizedException $e) {
@@ -127,6 +127,32 @@ protected function filterPost($postData = [])
         return $pageData;
     }
 
+    /**
+     * Filtering posted data without changing custom theme dates
+     *
+     * @param array $postData
+     * @param array $pageData
+     * @return array
+     */
+    private function filterPostWithoutDate($postData = [], $pageData = [])
+    {
+        $newPageData = $this->filterPost($postData);
+        if (
+            !empty($newPageData['custom_theme_from']) &&
+            date("Y-m-d", strtotime($postData['custom_theme_from'])) ===
+            date("Y-m-d", strtotime($pageData['custom_theme_from']))
+        ) {
+            $newPageData['custom_theme_from'] = date("Y-m-d", strtotime($postData['custom_theme_from']));
+        } elseif (
+            !empty($newPageData['custom_theme_to']) &&
+            date("Y-m-d", strtotime($postData['custom_theme_to'])) ===
+            date("Y-m-d", strtotime($pageData['custom_theme_to']))
+        ) {
+            $newPageData['custom_theme_to'] = date("Y-m-d", strtotime($postData['custom_theme_to']));
+        }
+        return $newPageData;
+    }
+
     /**
      * Validate post data
      *