The behavior that is shown in the demo is the expected one, because the maximized RadWindow is supposed to has the biggest z-index on the page. You can control this behavior, however, by setting the ShowOnTopWhenMaximized="false" property of the control. This setting causes the RadWindow's z-index to stay unchanged when the window is maximized. In addition, you can explicitly set z-index to RadCorols in order to cover some specific scenarios. This page contains
the default z-indexes of some RadControls.
All the best,
the Telerik team
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