Clefairy isn't affected by poison

[CaffeinatedJitterBug]

I've been using the clefairy you steal from the little girl in Mt. Moon, and I've noticed every time it's poisoned, it'll get the marker indicating it's been poisoned but won't take any damage from it in battle. It still takes damage outside of battle whenever I walk. I haven't noticed this issue with any other pokemon so far.