Bug 471884

SUMMARY
Some apps (e.g. Dolphin) behave very oddly when they launch maximized and are then restored by dragging the titlebar.

STEPS TO REPRODUCE
1. Open Dolphin, maximize it, close it, and reopen it
2. Observe that Dolphin opens maximized
3. Unmaximize Dolphin by dragging the titlebar
4. Resize Dolphin by its top-left corner

OBSERVED RESULT
In step 3, Dolphin is positioned with the cursor at the top right.
In step 4, Dolphin's bottom-right corner suddenly jumps to the position where you started dragging (the top-left corner of the window).

EXPECTED RESULT
In step 3 I expect Dolphin to keep the cursor in the same relative position, like when dragging to unmaximize a window that was not initially maximized.
In step 4 I expect Dolphin to not jump around.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
Probably related to bug 437089
Possibly also related to bug 434116?