Keith,
Sort of taking a stab here... I see you've filled out the info in the Image Rights section, which includes a copyright. But I believe the filter dropdown copyright is referencing the Models, Properties and Artwork section, which also has copyright information.
In my own catalog, my results are the same as yours. If I use the search option, and search on copyright = Kenneth W. Claar, I do get my copyright results. The copyright field in the Image Rights section is not indexed, but can be searched (see the Searchable Fields dialog).
My copyright field is patterned copyright symbol yyyy, Kenneth W. Claar, and the above search works, even though I omitted the symbol and the year in the search string.
This may not help you, but may explain the results you're getting.
-- Ken Claar