Home City not leveling up. Anybody know how to fix?

I'm working on the US challenges and have made it up to Mississippi, so I've played quite a few games. Most of the time, the HC of the civ I play levels up just fine, but sometimes it doesn't. I've played (and finished) 3 games with the Dutch, but the HC is still level 1. Same thing happened with the French, 3 games didn't level them up, but they finally hit level 6 on my 4th game. When I view the postgame after each map, it always shows that my HC for the civ I played has leveled up; always to level 6 from level 1. So the Dutch has reached level 6 three times now, but it never sticks! Every time I start a new game, they've reset to level 1. The French were the same until they weren't.

What's going on here? Why aren't they leveling up like they should? Is this a bug? Is there a fix? Please help.