Thank you for the provided information. As for the RadWindow, please excuse me for this. It looks like I was caught by the word "window".
The dragging issue can be observed on different occasions and in various controls. I don't have much information about the origin of this, but it seems that the XAML inspectors are interfering with the drag/drop events. I guess at some point the inspector is catching the mouse which stops the currently running drag/drop action in the WPF application.
To avoid this, you can disable the XAML inspector (the Visual Studio XAML tools in your case) and enable it only when you need to inspect something.
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