When you download something and choose to open it in LibreOffice, it will be saved in /tmp. If you choose Save As, the default saving location will be in /tmp.
I just lost a partly written exam that way. I thought it was on my Desktop, but oh no, it was in /tmp and after rebooting it's now gone.
The suggestion is to NEVER let /tmp be the default folder in the Save dialog, and to ALWAYS warn the user if saving something there.