I've been messing around with pick pocket on merchants. It seems, for me, that pick pocket will only work once per skill level, per merchant. I'll increase the skill level, pick pocket one item from merchants, and subsequently be unable to pick any other items off that merchant. The process repeats itself for other merchants.

If I then spend another point to train pick pocket further, I can steal another item, but only one more item... Am I doing something wrong? Is this bugged? I'm using the latest patch release.