It works for me.
Here are screenshots of the three cases:
Here is a screenshot of the >0 vl definition:
Questions:
- What happens if you copy the search expression from the vl and paste it into the search box (with no vl chosen)?
- What happens if you set the rating of a book showing no rating to 1, then to undefined? (Ooops -- you answered this one.)
- What version of calibre are you running?
- Does running Check Library make any difference?