Hello Patrick,
Thank you for the clarification.
In this case, the comment field's content might be disappearing since your address book syncs with the address book on the RU Server that doesn't have these changes yet. Could you please try signing in to your RU Server first and then adding the text to the comments field afterwards? This way, both address books will sync automatically and the comments should be added to the Server's address book as well, so the next time you run Viewer or sign in to your Server, the comment field should stay intact.
Please let us know if this works or if the issue persists.