When I activate the split window view and have doc A left and doc B right, clicking into and working in A or B is not reflected by the Binder pane document list highlight. I think it would be helpful if that was the case.
Right now you have the situation that I might be working in the right split window pane on document B but in the Binder document A (that is open in the left split window pane) remains highlighted.
I am not affiliated with L&L, but I believe the short answer to your request is: “It works the way it does by design, and in future versions will (for the most part) continue to work that way.”
If you want to get into the gory details of why L&L chose the current implementation, a very similar request was discussed at length over in this post:
Hopefully that helps you understand the design choice.