Only show menu level 2 from active trail (with option Show as expanded) I'm trying to do something pretty basic in my perspective, but I keep failing at this simple task.

My website has a main menu that is displayed on top of the page that is 2 levels deep (hence the Show as expanded). On the left toolbar it has another display of main menu, starting from level 2.

I have a main menu that looks like the following:

-link 1 (has option show as expanded)
--link 1.1
--link 1.2
-link 2 (has option show as expanded)
--link 2.1
--link 2.2


Problem now is that in the left toolbar all my level 2 links are always displayed, probably because I expand them. But I only want to view the children from my active trail. 

Is this possible at all with the current setup? When I deselect Show as expanded, my top menu doesn't show the second level (except when I click the first level first = active trail).

Another problem with this new (menu) block system is that I use a template to render my main menu: menu--main.html.twig but both my top and left menu use this template. Is there any best practice to separate the templates?
I also discovered that if "Show as expanded" is checked, the menu is displayed at sublevels where it should not appear. This patch fix this behavior:

https://www.drupal.org/node/2631468#comment-10792980