I advise that you examine the following help article: http://www.telerik.com/help/aspnet-ajax/window-troubleshooting-wrong-window-opened.html
. It treats a similar case - the properties set in the markup are not honored in some cases because actually a different RadWindow is opened. Could you check if this is applicable for your case and if the ideas listed there help? In any case - you can use the RadWindow's client-side API
to set its properties and control its behavior right after opening
it (I assume you are using radopen(url, wndName) since the URL is correct, so radopen() will return a reference to the popu).
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed