Sometimes the camera angle does not flip back from 90° to 45° when the city screen is left. This happens when the arrow keys are used to leaf through the city list and then clicking "done". See the debug.err file at http://pastebin.com/isAuJCwh. It also can happen when the city screen is ended with ESC (which I could not reproduce right now).

I reported this problem before, buried in my wishlist of UI improvements. This probably wasn't the most appropriate place. Please forgive me if I repeat myself.