postfix incorrectly complains about: do not list domain in BOTH virtual_mailbox_domains and relay_domains

Postfix regularily prints in its logfile:

  warning: do not list domain lists.hacksaar.de in BOTH virtual_mailbox_domains and relay_domains

However, that domain is not in the relay_domains. It was there for a short time after the upgrade to 14.04 (coming from 12.04), indirectly through mydestinations. But I fixed that. Still, postfix keeps complaining.

"postconf -n" outputs:

alias_maps = hash:/etc/aliases
append_dot_mydomain = no
config_directory = /etc/postfix
disable_vrfy_command = yes
local_recipient_maps = $alias_maps
mail_spool_directory = /var/mail
mailman_destination_recipient_limit = 1
mydestination = hacksaar.de
mydomain = hacksaar.de
myhostname = mail.hacksaar.de
mynetworks_style = host
myorigin = $mydomain
readme_directory = no
recipient_delimiter = +
relay_clientcerts = hash:$config_directory/relay_clientcerts
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_delay_reject = yes
smtpd_helo_required = yes
smtpd_recipient_restrictions = permit_mynetworks, permit_tls_clientcerts, reject_unauth_pipelining, reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname, reject_non_fqdn_recipient, reject_non_fqdn_sender, check_policy_service inet:127.0.0.1:12525,
smtpd_relay_restrictions = permit_mynetworks, permit_tls_clientcerts, defer_unauth_destination
smtpd_tls_ask_ccert = yes
smtpd_tls_cert_file = /etc/ssl/...crt
smtpd_tls_fingerprint_digest = sha1
smtpd_tls_key_file = /etc/ssl/...key
smtpd_tls_security_level = may
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
transport_maps = hash:/etc/postfix/transport
virtual_mailbox_domains = lists.hacksaar.de
virtual_mailbox_maps = hash:/var/lib/mailman/data/virtual-mailman