Did you do certain quest that raises that skill? <spoiler>
Hackdirt</spoiler>. The idea is that the stat increase you get is only a temporary 'boost' and not a permanent increase. I believe this applies to other similar rewards of skill bonuses.
So you get, say, 5 extra points as a reward, taking you from 14 to 19. Your skill
is now in effect 19, but in the background the game is still raising your stat from 14 to 19. So until you actually get those 5 points yourself, you won't actually see the skill increase. It's like a loan; the game gives you 5 points, but you've got to pay them back yourself until you can make any more. At least, I
think that's how this 'bug' manifests itself.
Thread:
http://www.elderscrolls.com/forums/index.php?showtopic=293533