Empty column options on agile board

Someone recently accidentally changed one of the enums used on our projects, rather than cloning.  After I changed it back, I see a bizarre artifact on the agile boards that use that field:



When I try to do anything to that empty box I get a warning about "Column <old value> not found".  Is there anything I can do to clean this up?  In the actual project custom field settings I don't see anything about the old value.

Thanks,