If I select "city overview", the first time loads and shows without problems, the second time the screen turns black (semi-transparent black, that is) and I have to reload the page. With other menus there aren't problems I think.
This bug comes back if one opens the town overview, and enters a town with one of those black triangles on the right of each town. Then if one clicks again on the town overview button, nothing appears, only the black screen.