[Gibberling Caves] Paladin Cleanses Heart, Acid Fog Happens

[Khazrak]

Was in the Gibberling caves last night on my half-orc paladin with a small group. Had a gibberling heart from killing the chief. Interacted with it in my inventory > chose to use the Paladin option to cleanse it.

The item was lost, but instead of getting a purified heart it just exploded in a cloud of acid that started eating everyone up.

Is this intended, or is this a bug as I suspect?