Ok. You've said that it was reverted to the start? then it's a C problem,
because it's handled by Tux:have_quest(), and Tux quests are stored in tux_t,
and tux_t is a C entity.

Now, the quest should not simply vanish. And indeed, it didn't. It's on the save
file. And marked as completed. So there is only one last thing: quest 'Tania
Sanity'.
The save file points that 'Tania Escape' handles everything and is completed.
So, the only way to this happen that I see is that 'Tania Sanity' quest.