dragging a window with mouse-click-hold does not bring it foreground/make it active
If you have several windows open and you start moving a window with mouse that is not front/active, it sometimes does move behind the currently "active" window, although I would assume that you moving a window would have made it active and brought foreground. More often happens when the currently active window is (borderless)fullscreen window, like mpv player (or some wine application), and you start dragging some other window from other display to the display where the mpv is/was active and the other window just disappears behind it.
workaround I have been using is that you just first click the other window you want to move and make it active and then with second click-hold start dragging it.
currently xfdesktop 4.18.1
; xfwm4 4.18.0
, but the problems have been around forever as long as I can remember.