[Dovecot] failing to deliver to one of multiple destinations

[Edgar Fuß]

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?