Steps to reproduce the issue

Download and install Joomla! 3.7 beta 3 with "Learning Joomla!" demo pages.
Enable modern routing with removing ID option.
Execute somewhere, e.g. in template view, the following code:

$route = ContentHelperRoute::getArticleRoute(8);
$sef = JRoute::_($route);

echo $sef;

Expected result

It must return the following URL:
/using-joomla/extensions/components/content-component/article-category-list/beginners.html

Actual result

Instead, it returns a URL with ID:
/using-joomla/extensions/components/content-component/article-category-list/8-beginners.html

Additional comments

Sorry if I misunderstood the new routing system, but for me it looks strange.