Some more info, I saw this thread and tried out Brian's idea:

http://www.xoutpost.com/bmw-sav-foru...nger-side.html

Unfortunately, it didn't confirm the logic of Brian's test. I don't know if that is because the ambient temperature was fairly warm (~75 degrees).

I also pulled the sensors out from the IHKA unit below the nav unit. This was actually easier than unplugging the white connectors. I'm pretty sure the sensors are okay because when I swapped the connectors the problem remained exactly the same.