Date of birth entry problem not validating

[Flyingfast]

I am filling out the Schedule A Background / Declaration IMM 5669E

Question 3. Personal Details of Parents.

I don't know the date of birth. Only the year.
In the filling out forms guide it says......

• If you don’t know a complete date of birth, use “*” (star sign/asterisk) to fill in the spaces for the year, month or day that you don’t know.

I have tried 1937-**-** and 1937-*-* and the form will not validate! What am I doing wrong?

Thanks
Pete