I had that problem in one game of mine, about six months ago. My logic-learning sim had to keep switching between the chess table and the telescope, or else his skill bar would get stuck, and sometimes that wouldn't help either. Sometimes it fixed itself upon me restarting the game, only for it to pop up again later. Other times, I had him travel to China and France, because it would get unstuck in a foreign land and he could raise his skills again.
I've seen it happen less often since patch 1.57 (I started getting the problem after patch 1.55), but when it hits, I usually take that as a sign to save, exit, and restart.
