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The described behavior is an expected one in the Windows 8, 8.1 OS versions. The IsRestricted property of RadWindow uses the OS margin restrictions which seems to be different in Window 8, 8.1 compared to Windows 7. We are not sure if this change was intentional one or a bug in the current versions of Windows 8, 8.1. From what we have observed it is possible to place any OS Window (for example the File Explorer) underneath the taskbar. If then the mouse button is release to stop the drag that Window is left underneath the taskbar and cannot be moved unless you interact with it's taskbar icon. Because RadWindow inherits some of its functionality from the WPF Framework's Window this behavior is also present in the RadWindow control.
Currently we are not aware of any workarounds to this as it is unclear if this behavior observed in Window 8, 8.1 is a false one or is an intended behavior in the latest version of Windows. I recorded a short video of the observed described behavior with both the WPF Framework Window and RadWindow instances. Hope this information is helpful.
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