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.