We couldn't figure out what was wrong with the quiz we had, so the instructor used the nuclear option:
- copy all problem paths into a text file
- delete quiz
- make new quiz with correct dates, and a bunch of empty problem templates
- paste problem sets back in, and save
This resulted in a working quiz.
Possibly related: we have periodic rerandomization turned on, but it causes all sorts of trouble with our database. (It's still useful enough to keep it, though.)
It used to be that requesting a new version of a question locked some settings in the database. Since last year, simply *viewing* a question is enough to have your individual version locked in the database, so that changes in the homework sets editor do not apply to your version.
Nobody else seems to be able to reproduce this bug though, and I have no idea what is different on my server.