I am not sure about this , but the terrain thingy sounds familiar to me , I had the issue once and figured out that the terrain min and max were empty directly after a terrain creation , it could be that the water surface (if it had waves) is when its created as a piece of terrain ?

then just after its created it needs the c_setminmax or something to update min and max or else they remain uninitialised .

will check it out of curiosity.