You could turn on Detailed Logging in CUPC, and then take a look at the uc-client.log file in the zip file that gets created when you create a problem report.
In amongst everything else in there, it should show some information about where it's getting its information from.
I used it recently to discover why we were seeing usernames showing instead of the display name. In our case it turned out to be because CUPC uses what it finds in 'Nickname' in preference to anywhere else, which in our case contained the username. Remapping that LDAP attribute fixed the problem, but if it turns out your one user is having the same problem then obviously it makes more sense to just change that user's Nickname field!