Email Address is being cleared for Ship To party Partner function in VA02 Sales order

Hi,

                I need to change Ship To  Address through programatically in VA01/VA02 transaction (Salesorder -SAPMV45A program) ,

Able to modify Address details like Company name,city ,country telephone number..etc  properly   using Function module , but observed Email Address is being cleared off after  my logic is being executed. 

i am using SD_PARTNER_ADDRESS_SET function module for Modifying Ship To partner address.

A new Address number (temporary number like : "WE &00001" ) is being created after passing to it.

i am passing Email Address also for this function module in parameters. Please help in this through your suggestions.

Thanks,

Vamsi