Hi Intruder,
This is going to sound stupid I know!
, but what the hell!
The alarm isn't wired in such a way that when the 'kill switch' is in the 'off position', that the alarm is being bypassed into being switched off itself is it by any chance?
Like I say, I know it sounds stupid, but isn't the first time I've heard of things being wired wrong even by professionals?!