Interesting!
Indeed it seems that it works correctly, if there is an empty line after the heading. But if there is none, it only works with 1., but not other numbers.
List starting at 1 (no space)
- Item 1
- Item 2
- Item 3
List starting at 4 (no space):
4. Item 4
5. Item 5
List starting at 4 (space)
- Item 6
So it seems that it’s more of a UX problem than a missing feature.