Duplicate Values in Bill to Customer LOV on Contract/Addresses Tab in Service Request Form

I have a customer setup with 1 primary bill to address but when i try and enter that on service request form --> Contract/Addresses tab.

It always shows me 2 values with same name and party number,

Can anyone tell me the logic behind this field

Tab "Contracts/Addresses"

Frame "Bill to Address"

Field "Customer"

I am attaching a screen shot as well.

Thanks

Kapil Kaushik