The selected value of a root menu is overriden by _process_breadcrums. For example, if the _is_selected function correctly determines that a root menu is selected by accessing a link which contains the root's url, when _process_breadcrums is run, the selected value goes back to False.

As a workaround for this issue you can use:
{% if item.selected or item.url in request.path %} active {% endif %}