Index: branches/5.0.x/core/admin_templates/incs/close_popup.tpl
===================================================================
diff -u -N -r12320 -r12478
--- branches/5.0.x/core/admin_templates/incs/close_popup.tpl	(.../close_popup.tpl)	(revision 12320)
+++ branches/5.0.x/core/admin_templates/incs/close_popup.tpl	(.../close_popup.tpl)	(revision 12478)
@@ -103,7 +103,10 @@
 			function window_close($close_callback) {
 				// use this instead of "window.close();"
 				if (!$modal_windows) {
-					if (getFrame('main').$.isFunction($close_callback)) {
+					// don't use other (e.g. parent) window methods to detect type of
+					// variables from given window, because it won't work in IE
+
+					if (Object.prototype.toString.call($close_callback) === '[object Function]') {
 						// use close callback, because iframe will be removed later in this method
 						$close_callback();
 					}