I think this duplication occurs every time after a sign-in problem. e.g.: I tidy up bookmarks or speed dial and when auto sign-in does not occur for some reason, duplication of speed dial, individual bookmarks and bookmark folders happens.
Very frustrating, as it would be a very useful thing if it worked properly.
I use only Opera and don't want to leave my login name for all to see here.
I think that I may also just forget this feature.