until you get a better reply,
it is likely PA config has allowed jack detection
module-jackdbus-detect.so (module-jackdbus-detect)
Not all sound cards have this feature.
Look at your configs, and I suggest you follow the wiki suggestion and use home user configs and comment out that module loading.
The advantage of home configs means you don't need to add any config files to your /opt/.filetool.lst
edit default.pa and comment out the following section
### Automatically connect sink and source if JACK server is present
.ifexists module-jackdbus-detect.so
.nofail
load-module module-jackdbus-detect
.fail
.endif
reboot to test and report what happens pls
When you disable jack detection, be aware that you sound levels for external speakers may be too loud for headphones and the reverse,
taking out headphones plugging in speakers may shock the people next doors?
2) You may like to provide some specs of your sound card?
3) And if its not too rude, have you tried just OSS or Alsa?
that is, why do you need PA?
no need to reply to that bit, I am not a big fan of PA
good luck