Index: wp-admin/js/custom-header.js
===================================================================
--- wp-admin/js/custom-header.js	(revision 22680)
+++ wp-admin/js/custom-header.js	(working copy)
@@ -17,6 +17,11 @@
 			var $el = $(this);
 			event.preventDefault();
 
+			if ( frame ) {
+				frame.open();
+				return;
+			}
+
 			frame = wp.media({
 				title:     $el.data('choose'),
 				library:   {