closing Popup fails in IE7

Issue Summary

Hello,
thanks for great module, I'd vote for this one to go in core (or at least as a standard) for 'boxes '...

As you can see from the title, I found that it's impossible to close Popup in IE *I am testing on version 7.
Of course after I finished testing my custom module and finished theming pop up window it all was great in firefox and Safari, one more check in IE and voila ! When I press Close button Pop up disappears but overlay stays.
Here is what IE debugger says:
Line: 607
Object doesn't support this property or method
Seems like this line:
Popups.popupStack.splice(Popups.popupStack.indexOf(popup), 1);

Since I am developing custom module and involve several js plugins I thought that it may be some conflict or whatever, than I minimized use of js and have only following loaded - and testing on popups/test path:
jquery.js, drupal.js, ajax_load.js, dhtml_menu.js, thickbox.js, jquery.form.js, jquery.cookie.js and popups.js.

Please check it if possible, I think it might be bug (as always troubles with IE !).
Thanks again, Nenad