Originally Posted by CitizenKhan
Beware of "flashies" - this is something I used to see a lot of on Far Cry user-maps, and I'm seeing it on Trials tracks as well.

"Flashies" is where you overlap two objects - if the overlap is exactly the same height, you get a flashing effect, as the game is trying to show both pieces simultaneously. The best way to combat this is to very slightly offset the items.
Fun tip: this is actually called Z-fighting