Reproduced in xenial by:
Swapping "quickly enough" between input sources of the same headset (Corsair HS40 gives Analog and Digital output). Also crashed the settings sound dialog. In-between crashing, the enumerated sources doubled.
Changing the volume too fast (my volume control is a wheel: Dell Y-U0003-DEL5).
Reproduced in xenial by:
Swapping "quickly enough" between input sources of the same headset (Corsair HS40 gives Analog and Digital output). Also crashed the settings sound dialog. In-between crashing, the enumerated sources doubled.
Changing the volume too fast (my volume control is a wheel: Dell Y-U0003-DEL5).