Comment 1 for bug 1312342

Same problem here. Attached external Monitors (different monitors and resolutions tested) through VGA or DP on my Notebook i experience problems with the mentioned screen placement.
The above screen works perfectly as long as the cursor stays on that screen. Wen I move the cursor down to the built-in screen, the above monitor starts to scroll between the screens.
I'm unable to move a window down to the built-in screen. Window-Title-Bar seems to hang at the bottom of the screen, also the rest of the window is shown on the other screen.

this short video demonstrates the problem: https://www.youtube.com/watch?v=7Qlkpe2MpNk

I once experienced this scrolling effect also horizontally (monitor to the right), but this happened only for a single screen session.

Editing ~/.config/monitors.xml manually resulted in the same problem, also when screens were placed using xrandr.
I also changed primary monitor (in monitors.xml) to the external one, but that had also no effect.

Sidenote (may or may not be important): I'm using nvidia-prima, which enables me to switch between graphics cars.
My System is a Lenovo Thinkpad T430 with two graphic cards a.k.a. nvidia optimus (DP wired to Nvidia 5400M and VGA wired to and Onboard Intel-Graphics Chip), problem happens on both ports.