Why does the case of city name change with suppler site api?

We are on 12.2.10 and have an interface whereby we take student vendor address info and call the ap_vendor_pub_pkg.update_vendor_site_public api in order to insert and update site addresses. When testing we noticed when we passed in a mixed case city name like Charleston, it came back uppercase, so we passed in uppercase to the api for city. After moving to prod, we noticed when we passed in uppercase it came back mixed case. We did more testing in test and there was a record with the city as CHARLESTON, so we updated it via the api with