Had two instances of the game suddenly quitting to DOS in the Kobold Cave. One happened when just one of my characters died of poison damage, and another just happened when an enemy wild boar died from Stinking Cloud. Needless to say, i'm pissed after having went through some long battles. Any idea what kind of bug this is and how to avoid it? Windows version by the way.

I think it's safe to kill them when they are helpless. IIRC the bug occured when the boars are in their second or third stage of regeneration.
Anyway they are relatively harmless compared to Trolls and Envoys, and they may even be affected by Sleep spells, which also favours saving them to last.

What's the status of this bug in other versions of the game?

I'll give that a try.

Still wondering why one of my characters dying from poison in the wilderness exited the game. I had cast Slow Poison on that character to revive it in the cave, but as soon as I got back outside to the wilderness and took one step, that character's health (which was almost completely full) drained to zero, died and then the game exited.

Never heard about that bug before.

Yeah, pretty strange. Thankfully I had a backup save right at the cave entrance in case of bugs.