3
This is a bug.
see
SourceForge Bug TrackerIn which the solution is described as:-
Dynamic Profile Field: Date type
When we create a date type field in dynamic profile,
modify /modules/profile/admin/user.php line 145 to
convert date string to timestamp as follows.
$user->setVar($fieldname, $fields[$i]->getValueForSave($_REQUEST[$fieldname]));
(Slightly modified as the original has some bold tags in it)