That's a bug :( We haven't seen it often but it does happen and we aren't sure why. It seems to go away if you restart the game.
I did,restarted and reinstalled,could it be grass texture or something ?
Seems to be all textures associated with the terrain only. Hmm.
Well if you get any idea how to fix it or what is issue,please contact me :Dbtw,great game and idea you got,there are lots of options to improve it and add more things but it all takes time and hard-work.Wish you luck with this game in future :D
Thanks! And you can be sure we'll do our best to try and fix it :)