Apple - Support - Discussions - Project File Never Saved ...:
"I worked on a project all morning, saving as I went along, and when I was ready to export a QuickTime movie, I duplicated the Sequence so I'd have a backup. Sequence 2 was blank with no edits in it. I went back to Sequence 1 and it was also now empty. I tried to revert, and went to all the Autosave copies, but all of them were blank with nothing in the timeline. So although I was pressing command S all morning and my project had a file name in the Browser window. no project file on my disk was ever saved and all my edits were lost."Final Cut Pro has been very stable and reliable for a long time. Today's experience shakes my faith in the current version.
I hope to gain some insight from the discussion over on the Appple support site.
The authorities have been notified.