As soon I added a collider to the trees the basic character starting to fall through the terrain. This is starting to getting very annoying. I do have the controller above the terrain. I also have a terrain-collider on the terrain as well. I thought this problem was fixed long ago?
No help?
Still no help? I have tried many times to fix this, but the controller is just messed up.
go too the terrain tools and check that the terrain collider is unchecked
I will try that and give Unity another change, science it`s the best stable and flexible future editor out there 
Guess what, it worked with the terrain collider on. I hope it will work as it should from now on
Good to Hear !