Folder expand/collapse is counter intuitive. In windows explorer, outlook, oe and probably most windows apps that I know of, when you click + or - beside a folder, it only expands/collapse the folder not actually selects it. You have to click the folder itself to select, which is the correct and expected behavior.
I find myself doing this a lot when I’m organizing my emails and the folder context is always changing when it should really stay on my currently selected folder.
Also related to this, when I drag an email to a folder, the folder it’s dragged to opens the whole tree below it!