When you are born on february 29th, the birthday list in a non-leap year does not show your birthday because there is no february 29th in that year. As a consequence your birthday is only shown once in four years.
It may be a better choice to show your birthday in the birthday list of february 28th in non-leap years, probably at the end of the regular february 28th birthdays with a special marking/note.
P.S. I am not sure whether this should have been issued as bug or feature request