EE 7.5.15

Channel A is a 'Listing' Channel. When I create a new entry, I have some_url title in the url_title field. Then I go to structure tab and for the structure url, I have some_structure. I save. I go back to edit it, and on the Structure tab, the structure url is some_url.

Channel B is a 'Page' channel. In that channel, I do the same thing, but after save, the structure url is- correctly- some_structure.