Comment 4 for bug 1474225

Just reproduced on arale too.

Steps to reproduce (actually something I do regularly):
  1. Open Settings
  2. With your right hand put the phone down on the desk to your far right.

In doing so, you will often find you're tilting it slightly to the left, which makes the phone enter landscape mode. However because it doesn't respond the the rotation immediately, it appears to be rotating itself the moment you've put the phone down.

So it's a simple matter of we're not thresholding the accelerometer adequately -- we're too sensitive to brief tilting.