Index: wp-admin/js/common.dev.js
===================================================================
--- wp-admin/js/common.dev.js	(revision 18163)
+++ wp-admin/js/common.dev.js	(working copy)
@@ -36,7 +36,7 @@
 
 	toggle : function(el) {
 		el.slideToggle(150, function() {
-			var id = el.removeAttr('style').parent().toggleClass( 'wp-menu-open' ).attr('id');
+			var id = el.css('display','').parent().toggleClass('wp-menu-open').attr('id');
 			if ( id ) {
 				$('li.wp-has-submenu', '#adminmenu').each(function(i, e) {
 					if ( id == e.id ) {