The issue occurs in the following scenario. RadWindow is the MainWindow and a button click opens new RadWindow instances with its Owner set to the MainWindow. You open several child windows and then close them. After closing the last child window, the MainWindows is not activated which brings it behind the previously activated application (lets say Visual Studio, because that was opened during the tests).

To work this around, avoid setting the Owner property of the child RadWindow instances. Or when the last child window is closed, manually activate the MainWindow by calling its Activate() method.