Birthday not saved at registration but saves when changed by admin in backend

Hey,

just discovered a strange problem on my site. During the registration the birthday does not get saved though I have all options set as far as I know.

When I login to backend as an admin, I can change the birthday and then it is saved and shown on the profile. Though this is no solution at all.

I searched the forums and found this:
http://stackideas.com/forums/birthday-field-is-not-work-with-format-dd-mm-yyyy-in-registration-page

But I tried to go for MM/DD/YYYY and it does not save either.