So this is the first version of Ubuntu that stops the sound from coming out of my speakers when I plug in headphones. Unfortunately it also stops the sound altogether... I would like to submit a bug report but I can't remember how, nor what program I should submit it for?
SnapOverflow
This question should have all the information you need about issues with alpha and beta releases.
In particular, this link covers how to report bugs.
As for what package you should file the bug report under, try to narrow it down as much as possible. If it only happens for specific programs, there's probably a common link between them. If all of your system audio is broken, I would file it under ALSA.
Found a workaround (for a Dell notebook):
Add the following line to /etc/modprobe.d/alsa-base.conf
options snd-hda-intel model=dell-m6-dmic'dell-m6-dmic' might be replaced with 'dell-m6' or 'dell-eq'