I'm not sure we should keep that one: I used reproduction steps provided by Thomas Mortagne but I actualy chose an "article template" when creating the new page, to see if it would be kept.
When I switch to another editor, apparently content of the template is kept, and if I check the actual request performed when switching it's a POST containing all the info:

So for me the info of the URL are kept, it's just that they're not present in the URL anymore.