[Dovecot] Duplicate message

I'm running dovecot on my desktop and using kmail as a client on my laptop.

I am very happy with this - I was previously running kmail under NFS, and this is infinitely better.

There is one small issue, which is not very important. I get a small number of messages apparently duplicated. This doesn't really matter, as there is a facility Folder=>Remove Duplicate Messages under kmail, and this deals with the issue easily enough.

I just wondered though why I get the duplicate messages, and if there is some simple way to avoid them?