/etc/logrotate.d/bacula does not work correctly if one uses the default configuration, because in bacula-dir.conf:

append = "/var/log/bacula.log" = all, !skipped

and in /etc/logrotate.d/bacula:

# Bacula logrotate script

/var/log/bacula/*.log {
    monthly
    rotate 4
    notifempty
    missingok
}

the logfile paths do not match. Furthermore the warning in bacula-dir in the Messages resource:

#
# WARNING! the following will create a file that you must cycle from
#          time to time as it will grow indefinitely. However, it will
#          also keep all your messages if they scroll off the console.
#
  append = "/var/spool/bacula/log" = all, !skipped

would be obsolete, if logrotate also would rotate the /var/spool/bacula/log on a monthly basis.

The logrotate definition should be changed to:

/var/log/bacula/*.log /var/spool/bacula/log {
    monthly
    rotate 4
    notifempty
    missingok
}