When you perform an AD Import the information from the AD gets updated in ServiceDesk Plus. Hence if you have made the changes to the Requester details in ServiceDesk Plus the information will be overwritten with the values in the AD. To avoid this you must either update your AD with the correct information or you can un-check the options Sites, Departments etc when performing an AD Import.
Note: Please take a backup of the database before making any changes.
Thanks,
K. Andrew Navin