Hmm, are you sure you have all the latest scripts uploaded. There is actually code in place when the moderators are displayed to only display a name one time even if it somehow happens to be in the database multiple times.
If you do have a few scripts not updated that could explain it.
Any modifications at all? I'd also check to make sure your session folder is fully writeable.
If all that checks out then you'll probably want to open up a support ticket so I can take a closer look.
