[fetchmail]Getting occasional "Query status=15" messages

I'm running fetchmail 6.2.2 on a Solaris 2.6 system via an SSH pipe to
the remote system where it gets the mail.

Mail is being collected successfully but sometimes (i.e. maybe one
connection in three) I get a "Query status=15" error from fetchmail.
This means I get duplicate mail as the same mail gets fetched again at
the next connection.

Can anyone suggest what the reason for this error might be and any way
to fix it?

-- 
Chris Green (chris(_at_)areti(_dot_)co(_dot_)uk)