Chozo

I've been following the Shadows chapter of Math for 3D Game Programming, but for some reason I'm ending up with a weird problem that I can't seem to find the cause of. Here's a screenshot of what I'm seeing:

http://i.imgur.com/At3Xa.png

The black lines are the shadow volumes for all of the objects in my scene, using a single infinite light source. They're all coming from the stencil buffer (I've dumped the depth buffer between my ambient pass, my shadowing pass, and my lighting pass and it's never modified after the ambient), but I don't understand why I'm seeing the volume instead of just shadows where they intersect geometry. Any ideas what's going on? I'm more than happy to post whatever code would be relevant if that would help. Thanks in advance!