BMW: GPS Display Problem

After installing a CD changer in my car, I have a weird reoccuring problem.
Sometimes the screen in flipped vertically. It's not up-side-down in the way
if you rotated the screen on the top because what should be on the left is
still on the left. It is only wrong from top to bottom.

Now in the process I did have to disconnect the GPS unit. Does anyone know
if there is a particular wire that would cause something like this so I can
help limit my search for the problem.

It is hard to diagnose cause it only happens about a quarter of the time.