Okay, so I think you can close it.

Yea it could be because it forced to spawn a lot of chunks in the same time but shouldn't they check if there's a decoration over water anyway?

Hi,
In my current game grass/rocks started to rendering over water and on every new discovered chunk its there. Save game attached. I have few mods and I thought one of them could do that (Radar with big scan range) or maybe it is not mod related but anyway I think that the game should prevent this ...