The attached scene contains a matte floor with a matte object on top of it, and a sphere above them which can be matte or glass. The only light source is an ambient occlusion shader provided in the ZIP file.
Maybe this is not a bug and only me doing something wrong with the parameters, but I didn\'t expect the results of the occlusion() lighted matte object to be different depending on the presence of a glass object somewhere else.
In case the issue is platform-specific, here are the render I get from the RIB: http://instinctive.eu/tmp/rt-bug-glass.png when the sphere has a glass surface shader, and http://instinctive.eu/tmp/rt-bug-matte.png with the matte surface shader. I'm using Pixie 2.2.6 compiled from sources on a FreeBSD 8-STABLE amd64.