If you put the diffuse pass of a cycles render into a viewer node, the output is corrupted (see attached blendfile).
If you setup up a scene like that from scratch without saving it and connect the viewer node to a diffuse pass that goes through a scale node, it crashes instantly.
OSX, 10.8.2, r52233
(i couldn't test with newer revision, because currently building doesn't work, apparently because of a problem with split_viewer or something)