Seems this is the way to go. I researched a little further and found out that the upgrade has indeed confirmed, however since the "native" reservation is a) in a different GDS (Amadeus) and b) on an OAL-ticket, that native reservation currently has two enties for the same flight, one in confirmed business and one for the same flight in confirmed economy.

Seems that the TA must resolve this by clearing up the original reservation in Amadeus and revalidate the ticket manually to reflect the change made by the confirming upgrade...and that is probably what triggered the time-change eMail and also the fact that the reservation on united.com does not show up as in R-class.

Greetings - Dirk