Ticket #27897: 27897.patch

src/wp-includes/widgets.php

@@ -1421 +1421 @@
                 // time() that sidebars were stored is in $old_sidebars_widgets['time']
                 $_sidebars_widgets = $old_sidebars_widgets['data'];
 
-                if ( 'customize' === $theme_changed ) {
+                if ( 'customize' !== $theme_changed ) {
                         remove_theme_mod( 'sidebars_widgets' );
                 }
 
@@ -1506 +1506 @@
         }
 
         $sidebars_widgets['wp_inactive_widgets'] = array_merge($lost_widgets, (array) $sidebars_widgets['wp_inactive_widgets']);
-        if ( 'customize' === $theme_changed ) {
+        if ( 'customize' !== $theme_changed ) {
                 wp_set_sidebars_widgets( $sidebars_widgets );
         }