Default changes on network printers after rebooting workstation

Network printers ( all HPs ) are named after colors, which puts Black at the top of the list alphabetically.  Users will set their default printer to the one closest to their desk.  Sometimes and for some people, the default printer is getting set to Black ( presumably because it's first on the list? ) It's not happening for everybody, and it doesn't happen all the time, but it happens enough that I want to know why and try and fix it.  

All users are using XP pro, sp2 and print server is Server 2003.  No group policy is configured ( other than if your workstation is in the OU, all printers are available to you )

Any ideas why it would get reset to the first alphabetically listed printer when they reboot?  I've looked through the existing questions, but haven't found anything that quite fits my situation.

Thanks!