Ticket #38953: 38953.patch

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

@@ -666 +666 @@
 
                 // Opens the panel.
                 open: function( menuControl ) {
+                        var self = this;
+
                         this.currentMenuControl = menuControl;
 
                         this.itemSectionHeight();
@@ -672 +674 @@
 
                         $( 'body' ).addClass( 'adding-menu-items' );
 
+                        jQuery('#customize-preview').click(function() {
+                                self.close();
+                                this.unbind();
+                        });
+
                         // Collapse all controls.
                         _( this.currentMenuControl.getMenuItemControls() ).each( function( control ) {
                                 control.collapseForm();
@@ -1320 +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;