Ticket #42173: 42173.0.diff

src/wp-admin/js/customize-controls.js

@@ -8381 +8381 @@
 
                 // Handle exiting of Customizer.
                 (function() {
-                        var isInsideIframe = false;
+                        var isInsideIframe = false, changesSinceSave = 0;
+
+                        api.bind( 'change', function() {
+                                changesSinceSave += 1;
+                        } );
+                        api.bind( 'save', function() {
+                                changesSinceSave = 0;
+                        } );
 
                         function isCleanState() {
+
+                                // Handle special case of previewing theme switch since some settings (for nav menus and widgets) are pre-dirty.
+                                if ( ! api.state( 'activated' ).get() ) {
+                                        return 0 === changesSinceSave;
+                                }
+
                                 return api.state( 'saved' ).get() && 'auto-draft' !== api.state( 'changesetStatus' ).get();
                         }