That happened to us by accident a couple times before figuring out what happened.
Seems the tribute aa for second chance, or whatever it's called. The one that saves you from dying, like the cleric spell.
When it activates, it not only saves you, but adds a DA effect.
Tank almost dies, it kicks in, and people start dying.
I think we blamed some bards for it, because no one had any idea hwat was going on, other than the tank had an invuln icon.