Hi, I have already updated to the 4.0.3 version, and it is not possible to highlight with the blue color any of the selections made with the mouse in the design panel.
I'm on the Mac version and it works just fine for me. The page that is open is already highlighted for me and to highlight more things just hold the Ctrl or Command button down and click something in the tree and it will highlight. I'm thinking you are probably thinking it will highlight when you click on it alone and it doesn't work that way. You need to hold the Ctrl or Command button down and then click.
Also you can only highlight things that you can actually change, meaning you can not highlight the jquery and boostrap.js files because you can't change them.
Saj