here's my super confusing and very long method, but if you have no other ideas you can try it:
why don't you sync your calendar with another calendar (google, whatever windows uses, mac iLife, etc), then restore all contacts to your phone from your backup, view the contact of interest from your phone, copy the contact of interest manually from your phone to the calendar you sync'd to, erase all contacts on your phone, then sync one more time to get your contacts back plus the contact of interest you just entered. whew.
