Ticket #38953: 38953.2.diff

src/wp-admin/css/customize-nav-menus.css

@@ -719 +719 @@
         opacity: 0.4;
 }
 
+body.adding-menu-items #customize-preview iframe {
+        pointer-events: none;
+}
+
 .menu-item-handle .spinner {
         display: none;
         float: left;

src/wp-admin/js/customize-nav-menus.js

@@ -665 +665 @@
 
                 // Opens the panel.
                 open: function( menuControl ) {
+                        var panel = this, close;
+
                         this.currentMenuControl = menuControl;
 
                         this.itemSectionHeight();
 
                         $( 'body' ).addClass( 'adding-menu-items' );
 
+                        close = function() {
+                                panel.close();
+                                $( this ).off( 'click', close );
+                        };
+                        $( '#customize-preview' ).on( 'click', close );
+
                         // Collapse all controls.
                         _( this.currentMenuControl.getMenuItemControls() ).each( function( control ) {
                                 control.collapseForm();
@@ -1319 +1327 @@
                         this.container.find( '.menu-item-handle' ).on( 'click', function( e ) {
                                 e.preventDefault();
                                 e.stopPropagation();
+                                api.Menus.availableMenuItemsPanel.close();
                                 var menuControl = control.getMenuControl();
                                 if ( menuControl.isReordering || menuControl.isSorting ) {
                                         return;