Postfix configuration bug

[Téssio Fechine]

Ubuntu 14.04's postfix (installed from mail-stack-delivery meta
package) configuration file, main.cf, comes with an odd configuration:

--=--
smtpd_recipient_restrictions = reject_unknown_sender_domain,
reject_unknown_recipient_domain, reject_unauth_pipelining,
permit_mynetworks, permit_sasl_authenticated,
reject_unauth_destination

smtpd_sender_restrictions = reject_unknown_sender_domain
--=--

Placing reject_unknown_sender_domain under either
smtpd_recipient_restrictions or smtpd_sender_restrictions has the same
effect.. but mail-stack-delivery's main.cf file has it under both,
which is redundant.
I think this has no purpose except for making the configuration file
more confusing, letting the user think reject_unknown_sender_domain
has two different purposes..