The RadWindow has the feature that you want and I recommend you to use that control in order to achieve the desired result. Indeed, you need to manually maintain the settings of the RadWindows, because they do not persist their state.
The flickering which occurs is not an expected behavior and I am not quite sure what is causing this problem in your case. Could you please send me a runnable project (you need to open a new support ticket) which shows the flickering behavior? I will check it and do my bets to provide a working solution as soon as possible.
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