The Mac Client only while hosting shows no buttons when transitioning between phases on a turn -- the game freezes requiring players to drop back to lobby and reload. This has been reproduced on 3 different mac computers (iMac 2010, Mac Mini 2009, and Macbook Pro Retina) with OS Lion and Mountain Lion. The map being played is Total World War (TWW).
Again, this only happens to mac computers when they are hosting.
Note: This also happens to the players with PCs connected to the game.