This bug might be hard to re-create. I opened a quest in 339, worked on it for awhile - new tiles, new combos, new screen, a new enemy, made a new script in the buffer.
Went to save. It went through the regular motions, but then said "Error saving." And sure enough, nothing I did was saved.
EDIT: Nevermind, the file somehow got changed to read-only. Fuck me.