I have not encountered this before and I am afraid that this may be a behavior of the bootstrap that we cannot change. RadWindow is the same in all browsers - an absolutely positioned DIV element with the given dimensions that is a direct child of the <form> element. The fact that such an element causes the framework to misbehave is not something we can influence. What I can suggest you try is setting some dimensions to the html, body and form elements to accommodate such a div and the other content from the page. Another thing you can try is setting the dimensions of the popup only after it is show via its Client-side API
(the setSize(width, height) method). You can also try storing the current browser size in the OnClientBeforeShow event of the RadWindow, then restoring that after the bootstrap has changed it. The isIE check and the getClientBounds() method from our static client library
can be useful for this.
the Telerik team
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