Kmail duplicated and invisible emails

I have finally got round to setting up 13.06, and very nice it is too. However, Kmail has a two duplication problems and one of invisibility. I copied the local-mail over from the previous install and initially everything seemed OK. Then I linked up Ubuntuone and it synced a whole lot of emails I thought I had deleted. Maybe the problem lies there.

  1. Seemingly randomly, the emails in a mailbox will be duplicated and even more, today I found a mailbox that I had set up the day before, and moved emails into, had 8 extra copies of every email. Yesterday I found all emails in a folder that had not been added to for a year had all been duplicated (just one extra). After I had finished deleting one copy of each the entire mailbox suddenly emptied. I have several mailboxes with duplicated emails, but I can’t be bothered going through and deleting them.
  2. A couple of times an email has been shown in blue, even though it has been read, and I can only send it black using the “mark all emails as read” option.
  3. Last night an email came in but there was no visible content. Today I can see the content.

Is this a known bug, and is there anything I can do about it?