Index: wp-admin/css/wp-admin.dev.css
===================================================================
--- wp-admin/css/wp-admin.dev.css	(revision 18873)
+++ wp-admin/css/wp-admin.dev.css	(working copy)
@@ -2302,7 +2302,7 @@
 }
 
 .sorting-indicator {
-	display: none;
+	visibility: hidden;
 	width: 7px;
 	height: 4px;
 	margin-top: 8px;
@@ -2340,13 +2340,13 @@
 
 th.sorted.asc .sorting-indicator,
 th.desc:hover span.sorting-indicator {
-	display: block;
+	visibility: visible;
 	background-position: 0 0;
 }
 
 th.sorted.desc .sorting-indicator,
 th.asc:hover span.sorting-indicator {
-	display: block;
+	visibility: visible;
 	background-position: -7px 0;
 }