When raising the terrain at the edge of the world in the Editor it results in a strange shadowing artifact as can be seen below. I've never noticed this before so I'm wondering if this is a recent bug perhaps.

   

This can also happen in game, when terrain raises and ends up at the end of last area.
BTW, can you check it with material culling enabled?

Interesting... turning culling off on the terrain materials solves the problem. This doesn't make sense as culling should not need to be switched off for these materials. They are applied to solid terrain, not leaves on a tree that need culling off.

As I said, this seems to be a new issue as I've never seen it before and I've never switched culling off before.

Anyway, there seems to be some light bleed or something going on with culling off that I've also never seen before. See below. I get the feeling something has gone funny recently with terrain shaders perhaps.

   

It's not a new issue, I've noticed this about 3 months ago... And actually, it makes sense, as lighting doesn't cast shadows through the polygon backface. And because your hill is cut in half, light falls exactly on these surfaces :-) Which results in such artifacts - they are not exactly a bugs, it's just a drawback of this lighting technique.

Somebody correct me if I'm wrong (I might be).

No, you are correct. I just don't recall seeing this before so thought perhaps it was a recent issue that has cropped up.

The light bleeding only seems to show up when raising the terrain at the edge, which supports what you said and I suspected. Strange that we need to turn culling off for terrain materials though.

Oh well, I guess we just work around it.

you don't need to turn culling off, just make neighbor areas