[Dovecot] sieve vs deliver -m

I'm invoking deliver through postfix with a dovecot transport in master.cf, using the -m ${extension} argument. If I have no sieve script, or a sieve script with an implicit keep, the mail gets correctly filed into the -m mailbox.

However if the sieve script has an explicit discard, this gets honored if it doesn't match another sieve action.

Shouldn't -m take precedence? I would say that if an extension is present any other sieve action should be ignored, perhaps just sieve_before should be run then the message filed per the extension.

-frank