Could be many reasons, most likely because someone made a map with the default objects groups altered.
For example, some people make their maps and they edit the default game objects groups wich cause these glitches.
Redownload the map and install it again.
Also, if at object maker you has been editing the default game objects groups like Miscellaneous, MyPlants, MyRocks, MyTrees and Default, you will get glitches like that.