Reactive - Keep submenu open after selection

I have a menu that contains a Submenu. This is implement as shown below;

Whenever I open the submenu and click on one of it's items the page opens but the submenu closes. I rather want it to stay open. 

Note that having it open by default is no issue, that's simply by adding the css class "open" to the ExtendedClass parameter. And I could of course create a whole elaborate mess of client actions and local variables to detect if I need to add the "open" class to the submenu but I was wondering if there is a nicer and cleaner method for this? 


note: No, this is not an advertorial in disguise. I really want to have a nice and clean solution for this problem and this application has and easy to share behavior of my issue.

I also noticed that by adding the css class "open" to the submenu you get a ugly flicker when you perform a page transition.