Comment 6 for bug 535491

I would argue that the sound and power management buttons are to do with the physical access to the device, and are more akin to physical actions like switching power on/off or pulling the sound cable, rather than accessing the session of a logged in user.

I accept your point that it is possible that that the user would want to block PM/sound controls when locking the screen, however I maintain that most often this is not the case.