[QT] First toggle of "Window on top" moves the window to the original position

Needs to be checked on other WM's, however the following ones do exibit this issue:

1. xfwm4
2. openbox

Steps to reproduce:

1. Launch the QT version
2. Move the window anywhere
3. Toggle "Stay on top"

Window moves to the original placement ( happens only on first toggle ). It should, obviously, stay where it is.

Investigate whether it's a bug in QT or WM's.