Index: wp-admin/css/nav-menus.css
===================================================================
--- wp-admin/css/nav-menus.css	(revision 31928)
+++ wp-admin/css/nav-menus.css	(working copy)
@@ -89,6 +89,7 @@
 .manage-menus select {
 	float: left;
 	margin-right: 6px;
+	max-width: 100%;
 }
 
 .manage-menus .selected-menu {