If that is related to creature dying to combat damage, while you took lethal damage, then that is not a bug. No life gain trigger can save you, because you lose before they even make it to the stack. Losing the game for having 0 or less life is a state based action, so is creatures having been dealt lethal damage being destroyed. Only after all state based actions of a check have been dealt with (simultaneously by the way, meaning at the same time), does the game even look at triggers to put on the stack.

This is different from lielink. Life gain from lifelink happens as the result of damage, so immedeately with the damage being dealt, no trigger, no delay. Hence why you gain the life before state based actions are checked, and would see you at 0 or less life.