Does anyone know how cultural borders work when you're on the same team as another player? By this I mean you have a permanent alliance.

At the beginning of my first permanent alliance game, I had several tiles where Cyrus (my permanent ally) had more culture. The tile was under my control though. I attributed this to the fact that the tile was inside the fat cross of one of my cities, and this was not the case for Cyrus.

In the latter game I saw some counterexamples though, like the one below. Does anyone know the rules on this?

http://img504.imageshack.us/img504/2286/civivallianceborderswd8.th.jpg (http://img504.imageshack.us/my.php?image=civivallianceborderswd8.jpg)

That's normal. In short, the engine selects whose tile it is by which city "needs" it more. Some tiles are more favored than others--which is seen by how borders expand. You may be able to select that tile that is Ethiopian by opening up your city management and click on the blackened tile. Forced working will probably take control of those tiles, but control will be relinquished when you stop working the tiles.