User Registartion -- Createdon date inserting wrongly.

Hi All,

           I am using sakai 2.6. I am getting a problem in User Registration. When users are registering, some users createdon date in "SAKAI_USER" table was inserting wrongly. i.e., createdon date inserting like 1/1/1970 0:00 ,12/27/2012 9:13 etc. i.e., some times the date is the previous date and some times the date is the future date. Did any one got this type of problem? If got, how to reproduce the issue again?
What would be the base cause?

Thanks & Regards
Bhanu Teja M.