Joplin ignores iOS

iOS provides a setting which allows or denies apps to refresh in the background, over wifi, or LTE. Joplin does not only seem to ignore this setting, it is able to refresh in the background even when this isn't allowed to any app at all.
Feature or bug ?

Joplin does not have a background sync on mobile devices. When Joplin is closed, sent to the background or the device is put into sleep (display off), the sync is interrupted.

This is not what I see happening on my iPad. It keeps happily syncing while in the background, there is no doubt about that.