Ticket #37697: 37697.3.diff

src/wp-includes/revision.php

@@ -594 +594 @@
                 return $value;
         }
 
-        if ( empty( $_REQUEST['_thumbnail_id'] ) || $post->ID != $post_id || '_thumbnail_id' != $meta_key || 'revision' == $post->post_type ) {
+        if ( empty( $_REQUEST['_thumbnail_id'] ) ||
+             empty( $_REQUEST['preview_id'] ) ||
+             $post->ID != $post_id ||
+             '_thumbnail_id' != $meta_key ||
+             'revision' == $post->post_type ||
+             $post_id != $_REQUEST['preview_id']
+        ) {
                 return $value;
         }
 

tests/phpunit/tests/post/thumbnails.php

@@ -242 +242 @@
 
                 $GLOBALS['post'] = self::$post;
                 $_REQUEST['_thumbnail_id'] = self::$attachment_id;
+                $_REQUEST['preview_id'] = self::$post->ID;
 
                 $result = _wp_preview_post_thumbnail_filter( '', self::$post->ID, '_thumbnail_id' );
+
+                $GLOBALS['post'] = $old_post;
+
                 $this->assertEquals( self::$attachment_id, $result );
+        }
+
+        /**
+         * @ticket 37697
+         */
+        function test__wp_preview_post_thumbnail_filter_secondary_post() {
+                $old_post = isset( $GLOBALS['post'] ) ? $GLOBALS['post'] : null;
+
+                $secondary_post = self::factory()->post->create( array(
+                                'post_stauts' => 'publish',
+                        )
+                );
+
+                $GLOBALS['post'] = self::$post;
+                $_REQUEST['_thumbnail_id'] = self::$attachment_id;
+                $_REQUEST['preview_id'] = $secondary_post;
+
+                $result = _wp_preview_post_thumbnail_filter( '', self::$post->ID, '_thumbnail_id' );
 
                 unset( $_REQUEST['_thumbnail_id'] );
-                if ( null === $old_post ) {
-                        unset( $GLOBALS['post'] );
-                } else {
-                        $GLOBALS['post'] = $old_post;
-                }
+                $GLOBALS['post'] = $old_post;
+
+                $this->assertEmpty( $result );
         }
 
         /**