Directional Light shining on invalid objects

I've been making considerable progress on my projects, and come across a few oddities. In this scenario, i have a terrain with an elevated mountainous region. At the base of said mountain, I have a cave system, some Depth buffering planes, a trigger to ignore terrain collisions, and a generic cave system. My light source is a directional light with Light strength 1, real time shadows, and a pinkish tint. My cave assets are one-sided meshes and all fit under the mountain. The front of the cave seems to work quite well when dealing with shadows, but the interior of the cave seems to be ignoring shadows cast upon them. I've even tried to place cube or spheres to case shadows to no avail. Does this have to do with the Terrain? Are there ways around this?