ToME: the Tales of Maj'Eyal

I was in the tunnels for the merchant quest and I opened a chest and was confronted with three enemies who immediately took down my shield and left me on the verge of death. Not unusual but it was my turn to act… so, I used my second shield rune and immediately died. WTF?

Instant or not instant? If it's instant then why did I die? If it isn't instant then it's labelled incorrectly… even if it's something ridiculous like 1/100000 of a turn. This is the only time this has ever happened to me over months of gameplay so I'm not sure what's up.

Any help?

It should have been instant.
However, I have noticed a couple of times that it doesn't always seem to notice you are dead until you press an action.

Well, that's certainly a possibility that I'd not considered… weird.

Either way, it was a bummer because I really liked that build and I'd already gotten past the hardest part of the start. So it goes...