Windows XP SP3, Outlook 2007

When I use the Quick Click to add a color category to a contact in the phone
list table view, it replaces the current category if there is only one. If
there is no category assigned, it adds the one I've selected for Quick Click.
If there are already more than one categories assigned, it adds the new one.
BUT, if there is only one category currently assigned, it REPLACES it with
the new one.

This certainly seems to be a bug! Any ideas?