Compiz Window-management: Maximized or horizontally semi-maximized windows (at least in a horizontal monitor configuration) jump monitors if focussed and on other viewport

During testing I found a new bug unfortunately, a multimonitor system is needed:

[How to reproduce]

1.Semi-maximize horizontally or maximize a window on monitor 2
2.Change the viewport
3.Switch back to your window with a switcher, or via click on its icon in a dock/launcher

[What you expect to happen]

The viewport changes and your chosen window on monitor 2 is focussed.

[What actually happens]

The viewport will change correctly, but the window will move to the main monitor and maximize/semi-maximize horizontally there.
WTF

Note:
The viewport switch itself does not even need to happen for the window changing its
position - the window will jump on the other screen, even if the viewport does not switch.

I've disabled a few plugins to make sure they are not responsible:
Cube Rotate, Grid, Move, Viewport Switcher and Wall are not responsible

I suspect this is a core problem, maybe hidden in:
PrivateWindow::addWindowSizeChanges (...)

probably
screen->viewportForGeometry or
screen->outputDeviceForGeometry

are responsible...

Reminds me of bug #776435 somehow...
(which also still needs fixing)