Steps to reproduce resize bug:

1) Compile/run the attached example.

2) Grab left-bottom corner of the MDI window. 

3) Drag to make the window smaller.

4) See that it works as expected (maybe with a bit of flickering, but that is reported in QTBUG-70974).

5) Grab right-bottom corner of the MDI window.

6) Drag to make the window smaller.

Expected: same as in step 4.

Actual: When trying to make the window smaller and not moving the mouse extremely slow, resize mode is exited and it is basically impossible to make the window smaller.

Steps to reproduce move bug:

1) Compile/run the attached example.

2) Grab window title bar just above the middle of the grey area.

3) Drag mouse downwards to move the window down.

4) See that it works as expected.

5) Grab window title bar just above the middle of the white area.

6) Drag mouse downwards to move the window down.

Expected: same as in step 4.

Actual: move mode is exited when moving the mouse with a bit of speed.

Small analysis of the bug: When there is a Qt3DWindow and a QWidget in a QMdiSubWindow the QWidget receives mouse enter/leave events, while the mouse is grabbed by the resize grip or titlebar in the QMdiSubWindow. The causes the QMdiSubWindow to stop resize/drag.