In 9.18, "*-source" is ignoring [port <integer>]
With configurations like
notify-source a.b.c.d port 12345; the "port 12345" declaration is ignored, and BIND uses random, different ports. This applies to all
*-source options as the reserved dispatches are only created and destroyed in
bin/named/server.c when parsing the configuration, but they are never used anywhere.
Support ticket 21617 refers.