Can't make floating windows stick to UI

When I click on the icon next to the close window/widget of ex. Recent Files I get a floating window, but dragging that window, doesn’t activate any hot zones to get that window integrated into the UI again. Isn’t this working properly now(it used to), or how do I do this correctly? I’m on Windows 8.

Having the exact same issue. I’ve found that double-clicking the title bar of the floating window seems to put it back into the main window, but often not where you want it to be. This is somewhat annoying.

I’m on Windows 10.

I’m on Ubuntu, with KDE5 on Wayland and I only see KWin’s title bar above the floating UI element, not Shotcut’s. So I can’t really double-click that to plonk the element back into the main UI…
Unfortunately I’m right now rendering a long video (~2h) so I can’t just switch to X11 to see if I can see Shotcut’s title bar there, as I then would have to stop the rendering and start it all over again.
Is there a keyboard shortcut to put a floating element back?
[EDIT]: Under X11 I could see Shotcut’s title bar and double click it to put it back. So it’s a Wayland compatibility problem.