When Poser saves a file, it sometimes renames the original to the pzSav_originalfilename form. When it's finished saving, this backup is deleted; if it crashes while saving, you can rename the backup to get your work back. It would be a wonderful feature, except most of the time the pzSav version isn't made, and I haven't been able to find out why. If you have Windows Explorer (or equivalent) looking at the appropriate folder while saving, you'll see these pop up from time to time.