Looks like PBEM has a problem. I have three games going currently (or had) and had the same problem on each. After about the third turn on one game we noticed that shields and surplus food were not being credited to the city in question. This means that the cities will never produce anything and will never grow. Is anyone else noticing this problem?
I've played a few single player games and things seem to be fine. Can't get any of the other multiplayer games to work, so I can't say if this bug affects those modes.