I changed my code to read the postgresql provider settings (host, admin username & pwd) no longer from Pulumi config but via a stackreference. After the changes, I get this as diff:

~ pulumi:providers:postgresql: (update)
        [id=6577980b-b7e1-466c-8a2d-18edaa0bc9fa]
        [urn=urn:pulumi:development::orthanc::pulumi:providers:postgresql::adminconnection]
        connectTimeout  : "180"
        database        : "postgres"
        databaseUsername: "psqladminun"
        host            : "<redacted>.<http://postgres.database.azure.com|postgres.database.azure.com>"
        password        : "[secret]"
        port            : "5432"
        superuser       : "false"
        username        : "psqladminun@<redacted>.<http://postgres.database.azure.com|postgres.database.azure.com>"

Pulumi reports a change to the provider, but none of the settings are different. Why reporting a change then?