The behavior from your first post is most likely related to the presence of more than one RadWindowManager on the rendered page. This scenario is discussed in the following help article: http://www.telerik.com/help/aspnet-ajax/radwindow-troubleshooting-wrong-window-opened.html
. Please examine it carefully, as it will shed some light on the behavior of radopen vs $find().show().
As for the postback - generally it should be avoided, just as you have noticed. Why it was working before I cannot be certain, but most likely it has been a partial postback (i.e. an AJAX request) that did not dispose the RadWindow you had opened, as it was created by a manager that was outside of the update panel that I assume resides in your UC.
the Telerik team
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