I've recently started checking non-cad files into pdm workgroup.  So far, these have included pdf's, edrawings, and zip files.  Some don't show up under the project and others do.  Whey trying again to check in the ones that don't display, I get a message saying the one that I'm checking in is identical to what's in the vault, and asking if I want to check it in again, anyway (implying it's already been checked in, even though I can't see it there).  What am I missing?