@jay - Depending on how you define a leaplings birthday this may or may not be an error

1 years, 0 months, 0 days between 2/29/2004 2/28/2005

This is how I define it

0 years, 11 months, 30 days between 2/29/2004 2/28/2005
1 years, 0 months, 0 days between 2/29/2004 3/1/2005