We do have hoods, which change the portrait to a "neutral" one. If logging out with this hood equipped, the original portrait gets lost (This is mentioned, when equipping the hood!).
I found, that the portrait storage was not implemented within the "Appearance Tool". I updated the scripts and removed the old database.
So: PLEASE use your "Appearance Tool" to save your current appearance again NOW (and also for each of your other toons the next time you use them). This way, the original portrait is stored, too, and if you loose your original portrait, you can recover it via this tool.
AKA TheOneBlackRider / An-Marcach