why does the Temple Runins crystal apocalipse not kill the party?

[lynx]

Remember the mirror and gem trick you can pull on the shadows before (ar1404) descending into the temple ruins? It has a wacky script (works as a repeatable trap), spshadow.bcs:

IF
  IsOverMe([0.0.SHADOW])
THEN
  RESPONSE #50
    ForceSpell(LastTrigger,TRAP_SHADOW_DEATH) // spwi023
END

Why is it wacky? IsOverMe is not mentioned in svtriobj.ids, so it's not a trigger that would set LastTrigger (AFAIK). This is why you can end up with shadows in the trap, that don't get zapped. One example is here:

https://youtu.be/mtuJSdRvnuI?t=8m9s (just after turning himself invisible, so not the best example)

 

What does set LastTrigger is the process of entering the trap (what Entered would check), so the way to zap all shadows is to lead them in and out of the trap, so LastTrigger has a good value once the trap script runs. Indirectly, almost by chance. This tactic is visible in the video and is required in gemrb.

 

The really odd part is that if the whole thing relies on side effects of entering the trap, then why isn't your party affected too, once they get over (and at least one shadow is still alive in the trap, so the trigger check succeeds)? That's what's currently happening in gemrb and I can't figure out what's different in the original. They could've put IsOverMe into svtriobj.ids and everything would still make perfect sense, plus the trap would be more effective. But no. Any ideas?

 

(maybe something for the fixpack, as I doubt it was the intention to be able to get to situations like in the linked video)