Picky Perkins,
"...All the evidence seems to suggest that the rudder problem with the FO had been sorted out..."
It evidently hadn't though. This is my point - we come across unusual/unsafe behaviour and hope/think we have sorted it, instead of reporting.
Don't get me wrong, I'm not for going behind someone's back but most of us wait too long before taking things further - myself very much included, I'm afraid.