Ticket #14979: 14979.2.diff

wp-includes/class-wp-customize-setting.php

@@ -425 +425 @@
  * @since 3.4.0
  */
 final class WP_Customize_Background_Image_Setting extends WP_Customize_Setting {
-        public $id = 'background_image_thumb';
 
         /**
          * @since 3.4.0
-         * @uses remove_theme_mod()
          *
          * @param $value
          */
-        public function update( $value ) {
-                remove_theme_mod( 'background_image_thumb' );
-        }
+        public function update( $value ) {}
 }