How to reproduce:
1. Download the attached project
2. Run Scene1 (There are 3 buttons. The top two buttons have their navigation type set to None.)
3. Click on each button and notice that top button doesn't stay selected. (Its navigation is set to none)
4. When the middle button is clicked, it has a specific Unity action to tell the EventSystem to make it the selected GameObject, so it does become selected. Otherwise, it would not be selected.
5. The bottom button, with automatic navigation, becomes selected when clicked as normal.

Expected: All three buttons should automatically become selected when clicked, or alternatively, documentation should make it clear that this behavior is intentional.

By design. Documentation needs accuracy.