Whee! I get to partially answer my own question. I'm on a Macintosh, and when the Mac version of Poser converts a hier file it also adds an ACTR resource to the OBJ geometry file which was converted. The ACTR resource is viewable through Resedit, and it contains a string of the path to the OBJ file (i.e. to itself, :Runtime:Geometries:myname.obj"). This ACTR resource is apparantly involved in whatever caching scheme Poser is using. Removing the ACTR resource made Poser take the full 20 seconds to convert the PHI file, and the resulting figure no longer contains the phantom Hose1 material. I have no idea why Poser does this, of where the cache of created cr2's is kept, but I've at least got a solution to my phantom materials problem.