I noticed that after deleting the twitter thing I had to setup everything again. The empty twitter data is still not in the source, so everything is green now.
Thank you for opening the issue, I think I can wait for a official fix. If I run into problems I know where I might find the answer. ;-)
BTW: This was the first release of WP SEO I installed. So there never was an upgrade.
Yes, the thread can be closed, I am doing this after I press "send". ;-) Thank you again!