FP2 and special characters ie umlaut, circumflex

Since installing FP2 on 8.5.1 client we have an issue with replying to emails from anyone who has a special character in their name. For example I received and email from Bernd Krüger/AT/ACME when I reply his name appears in the To: field as Bernd Kr?ger/AT/ACME and will not send. However if I pick his name from address book it appears correctly and is sent correctly.

Has anyone else experienced this?

Subject: yes…

… at least one user has the same problem here, but runs 8.5.1 FP3 Basic Client (on 8.5.1 FP3 Domino)