Open border exploit (could be a bug).

[BurnEmDown]

When I have open borders with an AI civ and they move military units inside my territory, I can't move workers and stuff to the tiles they're on. I'm not sure if this is a bug, but if not, it could be easily exploited by opening borders with another civ, moving a few military units into their borders, find out some useful tiles (like tiles with iron if they still don't have iron working), moving units onto each tile, and thus preventing them from improving the tile until the open borders are over. I'm sure the AI isn't even programmed to think about this in thinking whether to sign an open borders agreement or not, so you might be able to do it again after the agreement is over, if they still didn't improve them.

 

[Dark_Jedi06]

A civilian unit and a military unit can occupy the same tile, however for some reason they can't if they're from different civs.

 

[Dearmad]

oops. glad the beta testers noticed this and got it changed before release.

 

[Jaraxle]

oops. glad the beta testers noticed this and got it changed before release.

Having beta tested quite a few games I think its more likely that the beta testers noticed it wrote a bug report and for whatever reason the developers just didn't bother to fix it.