What is your operating system?
Windows 10 x64
What is your Shotcut version (see Help > About Shotcut)?
23.12.15 (also happens in older versions, tested 22.12.21)
Can you repeat the problem? If so, what are the steps?
New project, add a random video A to the playlist, then another random video B to the source player (also works with open other → colors).
Click&drag in source player window (this has video B) then release mouse button [inside the source player].
Expected: nothing happens, the original source video B was dragged over itself, right?
Reality: the currently selected playlist item (video A) is “dropped” inside the source player thus replacing the video.
This feels quite insignificant until you lose 5 minutes of filter work on a video only left in the source player that you wanted to drag and drop into the timeline but released the mouse button too early. 