I've searched a couple times topics talking about this bug, but i haven't find one.
So there it is:
When you are at the level or above the clouds (for example, when using the 7 button's cam mode or in the MT), you can see that the horizon fog is rendered in front of the clouds texture. And it's for all environments.
Some pics:
Actual version of TMCanyon:

An older version of TMCanyon:

Actual version of SMStorm:

Actual version of TMValley:

I hope that it will be fixed for the next update!
Regards,
Nerpson