I've been living with this for a long time, and figured I should probably write it up. I'm using Chrome mostly, don't know if it happens with other browsers, but here's what I see: if I go to City Overview to look over my production and vectoring, then pick a particular city out for whatever reason to look at more closely (buy production, change vectoring through the better interface, upgrade walls, etc), when I try to go back to City Overview the screen just locks up and I have to do a browser refresh to move on.
-Keith