Some maps have the default objects groups modified, these objects groups like:
Default, MyPlants, MyRocks, MyTrees.
When you install a map using a modified version of these objects groups, and then you install another map using a deferent version (either original or modified), then probably the objects will get messed up or not showing at all. This issue can be only fixed by the creator of the map, and you can deal with it by installing the map you are going to use just before to get on it. I know my be annoying to install the glitchy maps each time you want to go on them.