Respect list style of hierarchy

[Uroc327]

When changing the hierarchy with tab between numbered and unnumbered lists, the style only seems to be adapted in one direction:

1. test
2. test
3. test
    - a
    - b <Cursor>
    - c
4. test

Upon <S-Tab>, the line correctly changes to 4. b. But using <Tab> then doesn' change it back yielding

1. test
2. test
3. test
    - a
    4. b <Cursor>
    - c
4. test