I'm not going to include any unnecessary details here, just get straight to the point.

Basically, shaded/shadowed areas have no fade. Not even the old type where it was rough. Just dark as can be, and that's it. Here's a screenshot:

Strangely, in this one and ONLY in this one the lighting is affected too. Also for some reason it played cave sounds when I went in here.

It would only let me include one screenshot, but I took 5 others. 6 in total. It also happened under trees. For some reason, the bug only happened on certain objects. One of the screenshots included me showing how 2 trees were next to each other, one was normal, and one was buggy.

I've seen this glitch before in very early builds, but I had no idea it still existed.