I've tried to reproduce this bug on a couple of machines.
On Xenial, on a Thinkpad X270 - I don't have access to the "Internal Mic" when a headset is attached. Only a single mic is shown, and when I unplug a headset the volumes are correct.
On an Artful running GNOME Shell on a Dell Inspiron 11 - I do have access to the internal mic while a headset is attached, but adjusting the volumes as described does not recreate this bug.
Seems that it might be hardware dependent as well as a potential u-c-c issue?
I've tried to reproduce this bug on a couple of machines.
On Xenial, on a Thinkpad X270 - I don't have access to the "Internal Mic" when a headset is attached. Only a single mic is shown, and when I unplug a headset the volumes are correct.
On an Artful running GNOME Shell on a Dell Inspiron 11 - I do have access to the internal mic while a headset is attached, but adjusting the volumes as described does not recreate this bug.
Seems that it might be hardware dependent as well as a potential u-c-c issue?