Have you tried pming badspot about it?
Hata's Shader Toggle appears to fix this but you have to use his custom shaders but also slightly brights all shadows as a consequence; I'd like to know how to get it to work fine with port's soft shaders as well.
This doesn't solve it perfectly, but it helps.https://gist.github.com/portify/18d5e8de67f610e6fa92You can set the "opacity" of shadows on line 5. 1.0f is what everything looks like by default. 0.0f turns shadows off. 0.5f gives you a blend between the flat shadow color and the outside direct light.
Eh... it doesn't fix this issue? None of his shaders change anything about this.