It is reproducible (by me in Firefox) here. But if I change the poll type to Multiple Choice, it’s okay to insert, and then I can change it back and it’s okay to insert.
[poll max=2]
* Enter one poll option per line
* Enter at least 2 options
[/poll]
But the poll inserted is not a single choice poll…
This occurred for myself after testing the bug fix to the ranged number issue. It would seem that the value that appears in the type field isn’t truly set, if you change the type and then change it back again it sets it properly.
A little like having a Please Select option, with no valid value, but with the wrong name in this case.