Index: src/wp-admin/js/customize-controls.js
===================================================================
--- src/wp-admin/js/customize-controls.js	(revision 40289)
+++ src/wp-admin/js/customize-controls.js	(working copy)
@@ -564,7 +564,7 @@
 				}
 			}
 
-			if ( ! $.contains( document, headContainer ) ) {
+			if ( ! $.contains( document, headContainer.get( 0 ) ) ) {
 				// jQuery.fn.slideUp is not hiding an element if it is not in the DOM
 				headContainer.toggle( active );
 				if ( args.completeCallback ) {
@@ -571,17 +571,17 @@
 					args.completeCallback();
 				}
 			} else if ( active ) {
-				headContainer.stop( true, true ).slideDown( duration, args.completeCallback );
+				headContainer.slideDown( duration, args.completeCallback );
 			} else {
 				if ( construct.expanded() ) {
 					construct.collapse({
 						duration: duration,
 						completeCallback: function() {
-							headContainer.stop( true, true ).slideUp( duration, args.completeCallback );
+							headContainer.slideUp( duration, args.completeCallback );
 						}
 					});
 				} else {
-					headContainer.stop( true, true ).slideUp( duration, args.completeCallback );
+					headContainer.slideUp( duration, args.completeCallback );
 				}
 			}
 		},