Just a guess, but I would suspect they are. The N900 should automatically go into landscape mode when you open the hardware keyboard; also, I believe that it should hide the on-screen keyboard whenever the hardware keyboard has been opened. So, I suspect your N900 thinks that the keyboard is constantly out.

I don't know enough about hardware to say how to fix that, though. My understanding (from the battery wiki) is that the keyboard status is detected via a magnet somewhere, but that is the extent of my knowledge...