The best way to use the RadWindow is through its client-side API
and to keep it out of any postbacks (if possible), including partial ones.
All that being said, you can give the PreserveClientState
property of the RadWindowManager a shot. Note that it keeps the size and position of RadWnidows from its collection in a cookie, so it works not only for postbacks but for different sessions as well. Also, a cookie may be rejected by the client's browser.
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