I'm sorry it appears I misunderstood your initial post.
I see what you mean by shadows completely blacking out objects behind them and not colliding with them for some strange reason it's probably the way the shadow casting is set up instead of taking into account other objects the shadows seem to only take the object they are cast from into account when casting.
I tried a lot of things to try to find a workaround but I was unable to those shadows don't seem to care about anything I guess the current shadow system works better for, very specific top-down games or possibly special gameplay mechanics and don't work so well for visual appeal in a environment with lots of objects.
Unless is a workaround that i and you don't know of, anyways sorry for the misunderstanding good luck with your project.