Index: wp-admin/js/postbox.dev.js
===================================================================
--- wp-admin/js/postbox.dev.js	(revision 20614)
+++ wp-admin/js/postbox.dev.js	(working copy)
@@ -71,7 +71,7 @@
 				items: '.postbox',
 				handle: '.hndle',
 				cursor: 'move',
-				delay: ( $('body').hasClass('mobile') ? 200 : 0 ),
+				delay: ( document.body.className.match(/mobile/) ? 200 : 0 ),
 				distance: 2,
 				tolerance: 'pointer',
 				forcePlaceholderSize: true,
@@ -93,7 +93,7 @@
 				}
 			});
 
-			if ( navigator.userAgent.match(/mobile/i) ) {
+			if ( document.body.className.match(/mobile/) ) {
 				$(document.body).bind('orientationchange.postboxes', function(){ postboxes._pb_change(); });
 				this._pb_change();
 			}