When you start mythfrontend without the export EXPERIMENTALLY_ALLOW_PULSE_AUDIO=1 quirk, the second line of the output is
AudioPulseUtil: Suspend Success
and when you quit, the one before last is
AudioPulseUtil: Resume Success
So, in fact, mythfrontend is (successfully) suspending pulseaudio, which might explain why we don't get any sound after. Just my 2 cents
When you start mythfrontend without the export EXPERIMENTALLY_ ALLOW_PULSE_ AUDIO=1 quirk, the second line of the output is
AudioPulseUtil: Suspend Success
and when you quit, the one before last is
AudioPulseUtil: Resume Success
So, in fact, mythfrontend is (successfully) suspending pulseaudio, which might explain why we don't get any sound after. Just my 2 cents