Force pages to sort alphabetically

The docs say to number pages with a 0- in front in order to make the pages sort alphabetically. And I know about using num: zero in blueprints, but in my experience, as soon as I touch subpages they and all their siblings get converted to fully numbered pages. How can I force Kirby to respect the 0- in front and leave it alone?

Thanks.

When exactly does that happen?

I think it happens if I β€œtouch” the pages in any way. If I just click on a page and immediately press save, then suddenly the page and all its siblings go from 0s to numbers. If I go to the Edit section to make pages visible or invisible and drag anything anywhere then everything gets numbered.

I can not reproduce this and this sort of error seems to have occurred to someone else before, where the reason was - as it seems - a name mismatch, see this topic: Change URL in panel not sticking