Having fixed a problem with files getting stuck in memory over the weekend, I loaded up the new build and started taking memory dumps. They suggest that there's a handle leak from calls to StgOpenStorage and StgCreateDocFile. Since I'm watching the application and am reasonably certain that the files -- and their associated storages -- are actually getting closed, this is a bad thing.

I sent the dumps off to Microsoft support today and we'll see what they have to say.