Another glitch would be delayed grenade explosions. If I throw a grenade and duck behind a wall, corner, or back past a "Loading" point, the grenade will not explode until I come back upon it. It's almost like, if it isn't on screen, it isn't loaded to interact with the environment. Same with Flood forms. Only explode when I am close enough to it, and it is in my visual range.
On Assault on the control room, after you cross the catwalk that contains two banshees (where you try to grab one before the take off), with a wraith below, you enter another circular room with a central hub. In the center of this room contain four pipes coming out of the walls, two on one side and two on the other. You can hop in these tubes and run to the back of them. Two of these pipes have a brown "wall" at the back, blocking the back end of the pipe. You can run down the pipe and walk through this brown wall and it would have seemingly have disappeared. However if you exit the pipe and look back down it, the brown "wall" remains.