Just did what I was asked for xD..
I know users with outdated hardware had this issue in the past with african grass everywhere, and some others that played around with the map maker/object maker also managed to set it like this.
If I were you I'd just reinstall the game completely with a new installer without adding anything into the game(maps, objects etc) before you know if it works or not. And if it would work, you could add the custom things one by one and pinpoint if they were the problem.
And if that doesn't sort it, the ogre engine for the game did get updated to a newer version, so who knows, maybe it could have an impact on some systems.