Steps to reproduce the bug: Create a bunch of complex prims (twisted, hollowed, revolved torii), and a .01x10x10m wall to block them. Move the camera behind the wall in 3rd- and 1st-person (mouselook mode) views. Turn on on debug > rendering > info displays > octree.
Observed results: Occlusion rendering is inconsistent. Sometimes it culls, sometimes (most of the time) it doesn't--especially if in 1st-person view. Wear a large 10m3 invisible prim and compare in camera views to see. The same things culled in 3rd-person view aren't in 1st-person view.
Expected results: Consistent occlusion rendering.