I can't find any instances of %%s anywhere. Can you tell me where you found it and/or what you did?
I did find a mistake in the defaults in the DB files where it set the format to have a %f instead of a %N and have fixed that but can't see anything else wrong in that area.
Just to clarify, the database thing Phil mentions is the default value for Monitors -> LabelFormat column in the zm database. Just change the %f to a %N using your favorite MySQL editor (phpmyadmin or webmin are my personal favorites) and you'll be fine. (the fix above overrides that default value anyway, but never hurts to be on the safe side).