Created attachment 159570 [details]
[Wayland] Grabbing down a maximized app for the first time shifts its window top left corner to mouse pointer position

Steps:
1) Open Dolphin, then maximize its window and close it.
2) Reopen Dolphin again then grab its window from the middle of the titlebar then move it down

Observed result:
The window quits its maximized state, but the window top left corner is positioned at the new mouse pointer's location

Wanted result:
The window quits its maximized state and the new mouse pointer's location should remain at the middle of the titlebar

NB:
This happens only for the first grab, if you re-maximize the window and grab it down it won't happen.
The same bug is valid Qt and GTK apps.