[Jack-Devel] Can pulseaudio-module-jack "auto-start" jackd1?

Hi all. I'm running jackd1 (0.125.0) on debian 9 (stretch) and its "auto-starting" facility works perfectly whenever I use jack-play. I now want to use pulseaudio-module-jack, but "pactl load-module module-jack-sink channels=2" fails (the command returns "Failure: Module initialization failed" and I see "jack_client_open() failed" in the journal). Is this a bug, or is it "intended/expected behaviour"? (I don't understand how jack-play starts jackd1. Is it dbus magic, or something else?) Many thanks, Jaime