Some bugs crawling on the terrain need to be squashed.
1: Sometimes, if the terrain is steep, and you try to go over the hill, You'll still be going up an invisible vertical "surface", even tho you are way over the hieght of the terrain (talking 20-50 meters of height). This was a lot worse in 1.2 tho, big improvment over the terrain bug similar to this in 1.2.
2: One more bug (not really that important), is that when editing the terrain that clashes with the endless, invisible planar beyond the edge of the map, the terrain greatly distorts there. This did not happen in 1.2
3: Haven't tested this in 1.3 (Probly not that important either). When moving a gun spire, it steadily raises up off the ground, taking terrain with it. If this is done at the max height setting, the terrain under the spire will break. This happened in 1.2, but not sure about 1.3.
There may be one more, but I'm not sure of it. I think it's more of a hitbox bug. It has to do with a vehicle's braking, and weapon kick.
Edit: Also, terrain, and other buildings and objects, seem to be slightly transparent if you look hard enough. The Terrain's transparency is less noticable when it's on low.