Contacts birthday can't be removed

I have a list of 200 contacts. I do not know the birthdays of most of them. A large number of them have the null birthday value, 1/1/1601, in the birthday field as viewed when the individual contact file is opened. The select box is checked to use this as the birtdhay. When I unselect the box and hit OK then reopen the contact, the save is not changed. The box is still checked when the contact is reopened. If I change the date of the birthday, that change is saved. However, if I reopen the contact and uncheck the box and hit OK and close and reopen, the box is recheck and the date is returned to the null value date 1/1/1601. To add to the mystery, if the date is set to the null value then it will not display in the Contact folder Birthday column. I need to have the birtday field deselected and properly saved. Otherwise it creates problems syncing with other devices by either sending a null birthday value to the device when no birthday should be present or by preventing the device from sending to the PC a real birthday value since the PC thinks one already exists.

I have confirmed that the birthdays are not save in any other organizer on the PC, like Windows Calender and the files are not Read Only.

I have attached some print screens for clarity.

I have found a temporary partial solution.

Vista's Contacts folder can export all contacts to a CSV file. This export does not include the Birthday field. Exporting to CSV and then Importing the same CSV produced a list of contacts with all contacts having the Birthday field deselected. Unfortunately this removes any real birthday data as well. Fortunately for me I didn't have many birthdays stored in my phone. After resyncing my phone, this method has at least removed the 94 alerts on my phone for peoples birthdays coming up on the 1st of January.