I'm a little surprised that no one else has any comment on the problem, if not the solution. I used a couple of file recovery programs to get everything back, so that turend out okay. Well, that and having a two week old backup - still a couple of hundred files had to be recovered.
But am I the only one who's seen this sort of disk interaction when using a shared directory with XPM? I can say with great certainty that the files in that directory were gradually erased every time I did a file save to the same directory from within XPM (I could tell from the file write times and the timestamps of the deleted files).
Is it not possible to set up XPM to use part of a host disk?