Dovecot LDA error - Invalid -f parameter: Invalid character in path

[Bruno de Paula Larini]

Hi list.
I'm using dovecot as postfix's LDA. The version is 2.3.6.
Last week some spammer set the envelope's FROM to "foo at bar@domain.com" 
(with two @). While trying to deliver (as this one didn't hit the 
spamassassin's score), dovecot said the following:

Jun 21 02:35:58 mymailserver postfix/pipe[29736]: ADA268195E: 
to=<user at mydomain>, relay=dovecot, delay=0.08, delays=0.03/0.02/0/0.04, 
dsn=5.3.0, status=bounced (command line usage error. Command output: 
lda: Fatal: Invalid -f parameter: Invalid character in path )

Which caused postfix to put it on the bounce list, but the spammer's 
destiny don't really exist.

I could successfully mimic the spammer using telnet and putting two @ in 
"mail from" address.
I don't think this should be an expected behaviour, right? Or is this 
some config based error?

Thanks!