Using the module "Menu Item Extras" I added a field to menu links.
(I did that in order to use a translatable picture as a link label)
Adding a field breaks the rendering of the menu, which then appears as a bulletted list instead (see screenshot).
If I remove the field (keeping the Menu Item Extras module still installed), the menu display is normal.
apparently, the required classes are not being applied to ul and li elements.
Closed: works as designed
1.0
Code
menu item extras uses its own menu template, that's why the menu didn't get the proper classes for Solo.
so I will have to create a Frankentemplate that supports both.