IP not being awarded

Every so often, after I play a game and receive X amount of IP for the game, it doesn't appear on the top right of the homepage.

I recently played a game as Vayne, and the IP from that game would have been just enough to let me purchase another champion. It wasn't awarded however, as in my IP remained the same as if I hadn't played the game at all.

Is anyone else noticing something like this?