Just played a game where I used Karn, Scion of Urza +1 ability to have my opponent pick 1 of 2 cards to give me and 1 to exile under Karn with a silver counter. Ability resolved without a hitch but then during my next turn, it skipped my draw. Thought it was a wierd fluke and didn't happen again till I +1 again in the game and then realized it was Karn's ability that seemed to be causing it.