strange behaviours with sender_dependent_default_transport_maps

[zorg]

Hello
let me explains
Reading the manual, it explain that  
sender_dependent_default_transport_maps override default_transport

first I want to white-list sender address allow to sender mail to other 
domain

so fisrt I did that

in main.cf

    default_transport = error:error message
    sender_dependent_default_transport_maps = 
hash:/etc/postfix/sender_dependent_default_transport_maps

with /etc/postfix/sender_dependent_default_transport_maps containing

    postmas...@domain.com smtp:

In this case all my sender get the error


then I try

in main.cf

    default_transport = smtp:
    sender_dependent_default_transport_maps = 
hash:/etc/postfix/sender_dependent_default_transport_maps

with /etc/postfix/sender_dependent_default_transport_maps containing

    postmas...@domain.com error:message_1

It work like expected
if sender is  postmas...@domain.com i get the error with message_1
and all other sender can send mail

to finish i try

in main.cf

    default_transport = error:message_2
    sender_dependent_default_transport_maps = 
hash:/etc/postfix/sender_dependent_default_transport_maps

with /etc/postfix/sender_dependent_default_transport_maps containing

    postmas...@domain.com error:message_1

all user sending message get message_2

So what I understand is if the default transport is set to error the 
postfix override it whit  the sender_dependent_default_transport_maps value

Don't know if it is a bug or me that miss something

Thanks