Could you describe in detail what you've done since I never encountered such a situation. Have you seen it getting hit / taking damage? What was hitting it? Which bot was getting destroyed?
You might be right about the random super-nasty... it might have just been pure coincidence that it happened the first game session after installing 2.2 mod.
The bot that dies is the one that sprays spectral mines/bombs everywhere, phasing the baddies.
It dies a second before I did in that Upper Thames section. I didn't see it getting hit, just hears that fizzy crackle and saw the icon disappear just before I became "xxx headstone"
It might just be that the invulnerability is a super-high hit point and a baddie dealing 3500 hits on one blow might have given it four or five blows before it smacked me.
I'll investigate some more with 2.2 and see if I can repeat these events.
Edit:
Yes, since 2.1 I sometimes get bots die - first it was the phaser bot (bomber?) then it was the rocket bot. It does take a butt-load of damage; I'd estimate perhaps 40 000 health hit.
I've also noticed an increased damage dealt by enemies - a couple of times it's been two solid 2000 point hits and ... I'm dead.
Interestingly enough, I also have a hacked 2.2 and I set the sniper fire rate to 100/min.
With the sniper-screen-shake disabled, that is FUN - like a machine sniper gun.. haha.