Haha oh god, Backwash. The map that was so visually unoptimized, they removed grenade starts from it. Then the shitty Xbox 360 backwards compatibility couldn't handle it, so it was just outright removed from playlists. Nicely done.
The 360 emulated it fine up until someone picked up active camo. All they had to do was remove camo from Backwash in matchmaking, but I guess they found it easier to just remove the map.
It was hilarious though, because if you selected it way later in Halo 2's run in customs, people that had picked up Halo 2 later on would seriously ask me if it was new DLC