STO Address is copied from Supplying plant -- Check T001W-ADRNR... If you have created your plant as Vendor than check what is address maintained in vendor master.
Now if you change the address in STO Header, means new address is generated which will saved in PO header in ADRC table., System will not change data that you have in T001W for plant or Plant created as Vendor
Have you configured your STOs up to SLOC level ? if Yes then let everyone know so that we can explain more precise..