I am not quite sure what exactly is your scenario, but in general, although RadWindow looks that it is a child of the restriction zone, it is actually in a different place in the DOM tree. In addition the browsers have different implementation of the onresize event - for example IE fires it for every pixel while Firefox fires onresize when the ending has finished.
We will need to have a better view over your scenario and setup in order to provide you with appropriate answer. Please open a support ticket and send us a small sample project along with detailed description of the desired behavior. We will check it and if possible - provide you with a solution.
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