If you add the "Extend" page as a shortcut (using the plus icon next to the page title) and then add "Configuration" afterwards, the shortcuts in the shortcut bar in the toolbar should appear in the order in which you added them.
However, instead "Configuration" will appear before "Extend". I believe they are being displayed in alphabetical order by default, which doesn't really make sense.
Furthermore, if you then go to the shortcut administration page, you'll see that the links are listed there in the order you added them (not in alphabetical order). So the administration page and the reality don't match.
This occurs in Drupal 8 only (Drupal 7 works correctly).