Aha, interesting. I can reproduce the crash, and also introduce a method for reproducing it. There's two features of the engine which allow this to happen:
1) Casting Lock Melt to unlock a door will not trigger a trap
2) NPCs can open trapped doors without the trap going off (and incidentally can walk through the trapped square without it going off, as well).
So, you cast Lock Melt to unlock a door, wait for an NPC to open it, and then you can trigger this bug. Really it should possibly be one of those that needs to get fixed, rather than the actual crash, because really the trap should go off for the NPC (or during the Lock Melt), though of course fixing crashes is a good thing regardless.
I used my editor to re-close that door properly for you, btw, so it will work as-expected; I also moved that poor, confused Town Guard back outside the house where he belongs. Here you go: http://www.sendspace.com/file/1gq50p
BW, here's a save (slot20) where I've Lock-Melted the door and hacked an NPC inside, who will eventually try to head out of the house, and will open the (trapped) door by doing so: http://www.sendspace.com/file/41bjlg