Corispondent call in Thunderbird using threaded view

[Linux for blind general discussion]

Hi all,
Tried to send this yesterday but sent from the rong account.  Anyway, Using an exchange server with thunderbird, I am seeing a very strange item called corespondent call when using threaded view in all of my folders with the exception of the inbox.  Any one know how to get rid of this?  Disableing threaded view resaulves this, but get alot of messages and so would rather not have to do this if I can avoid it as some of the folders I have get alot of messages.  

Thanks all.