(as a little aside, there seems to be a ANOTHER protocol droid very close to C3PO and Leia during that final ‘group’ shot - a RED one as it happens…and if C3PO sticks to his gold arm in future without any kind of explanation about it in the next movie, then I might just as easy imagine that it had something to do with that particular droid, for some unknown reason!)
Bizarre Droid Marriage Customs, are Bizarre.