Adding spamassassin to postfix causes sender_bcc emails to triplicate

I have had a well working postfix/dovecot mail installation at home for a couple of years. To ensure all outgoing mail gets saved, I have sender_bcc_maps = hash:/etc/postfix/sender_bcc in my main.cf file

There are entries in that map file of the form alan@myemaildomain alan+saveout@save.save.

There are entries in /etc/postfix/transport of the form save.save lmtp:unix:private/dovecot-lmtp

And dovecot has a sieve file which is processed first with the following require ["fileinto", "envelope", "subaddress","date","mailbox","variables"]; if envelope :detail "to" "saveout"{ if currentdate :matches "year" "*" { set "year" "${1}"; } if currentdate :matches "month" "*" { set "month" "${1}"; } fileinto :create "Sent/${year}/${month}"; stop; }

My wife was moaning that too much spam was coming through (I have been also using dspam between postfix and dovecot but I think its been fairly untouched for a while) so I decided to add spamassassin using the recommended approach of adding it as a content filter to incoming messages to the master.cf file in postfix, ie changing the first line to smtp inet n - - - - smtpd -o content_filter=spamassassin and adding at the end of this file

spamassassin unix - n n - - pipe user=debian-spamd argv=/usr/bin/spamc -f -e /usr/sbin/sendmail -G -oi -f ${sender} ${recipient}

Now everytime I send an e-mail I get three copies of it in my sent-mail folder (obviously previously it worked with just putting the one there).

I am both trying to get my head around why I should suddenly get three copies. I suspect that something to do with spamassassin getting invoked for the send to alan_saveout@save.save in some way, and postfix adding ANOTHER sender_bcc entry.

Has anyone else experience this, and what is the solution?