Hi gingerlucy,
I had/have the same issue with duplicate bookings and an unconfirmed seat. I think it has something to do with there initially being separate PNR's from Finnair and BA if booked via ba.com but the PNR's were merged into one a little while ago and for some reason, it left the duplicate entries within MMB. I also had an "unconfirmed" seat so I called Finnair to check if there was a problem. They were incredibly helpful and could see there was an issue (which they couldn't quite understand or explain) but said as One World Emerald, the seats should be showing as confirmed so they pressed a button and all was fixed within minutes. Might be worth giving them a buzz as well just to be on the safe side.