Duplicate rows when exporting event participants

I have an active event set up with online registration. The online profile includes a participant note. The event also allows multiple people to sign up at once. When I use the CiviEvent dashboard to find registered people, I can use the action "Export Participants" and use a custom mapping, I can successfully export the information. But if I add "participant note" to the custom mapping , then I get duplicate records for some but not all of the participants.

Export Mapping that works: first name, last name, internal contact id, email

Export Mapping that breaks: first name, last name, internal contact id, email, participant note

This is using CiviCRM 2.2.8 with Joomla 1.5.14