Mixing unordered lists and ordered lists gets you a list that follows the first list element to decide if it is an ordered or unordered list on the preview, but on the resulting post, you get a sublist of the second type inside a list of the first type.
1. First line 1. Second line - Third line
...is shown in the Preview as:
1. First line 2. Second line 3. Third line
...but after posting is rendered as:
- First line
- Second line
- Third line