Alexstrasza the Life-Binder damaging friendly character

I was playing an arena game, my hero was on two health, and thought I’d use my Alexstrasza the Life-Binder to heal myself up. However, upon casting it on my hero, it instead dealt 8 damage to me and killed me. Pretty sure the tooltip says that it’s supposed to HEAL friendly characters, so looks slightly bugged to me.

what class were you playing

what was in your hand

what did you have on the board

did you by chance play this
Rare · Minion · TITANS · Battlecry: Your next healing effect deals damage instead.

There are effects in the game that convert healing to damage.

Presumably you played one of those prior to playing Alexstrazsa.