How to get true intersection of shapes

[Contours]

I have a shape with a shadow effect. I want to crop the shape by using the Intersecting Shapes method, so I place a rectangle over the area I want. The method works fine ... for the primary elements. But the full shadow gets carried over to the resulting shape.

One of the main reasons for cropping the shape is to lop off the end shadow, but keep the shadows in the other dimensions.

How might I accomplish that?