[Dovecot] failing to deliver to one of multiple destinations

Is it defined whether, in case a message should be delivered to
multiple destinations via a sieve script, and one of those
destinations fail, then the whole delivery is to be considered as
successful or not?

My case: A sieve script forwarding to and external destinations plus local keep. The keep fails (configuration error, wrong homedir, .dovecot.lda- dupes not writable). According to postfix logs, dovecot deliver returned success. The mail was NOT delivered to the local destination and NOT bounced.

Is this expected behaviour?