Number wrapping stops working with mixed lists

[willthong]

1. Multiline number indents work great normally; this line will be indented
   appropriately with ``gwip``. This works across many different lines. This
   work across many different lines.
2. And it also works across many different numbered items. And it also works
   across many different numbered items. And it also works across many different
   numbered items. And it also works across many different numbered items. And
   it also works across many different numbered items. 
3. Then an unordered list to mix things up:
    * I have ``textwidth=80`` on
    * I have ``set formatoptions=jtcqln`` on
4. Back to the numbers, but now we've lost the ability to wrap properly.
Correct indentation is applied while typing, but when we return to normal mode
and type ``gwip``, we get this undesired outcome.

Would hugely appreciate any help or thoughts - thanks!