Do you have powerlaunch installed or something else that might change MCE's behavior?

The click boundary extends from the top of the value to the bottom of the volume box (40x40 pixel box). It will be 60x44 in the next release but it also suffers from the same delayed update problem that everything else has so you may be clicking it but X doesn't update the window to show the change and you think you didn't click it.

The dsp, esd and media-server services can't be unloaded (yet) so sound will continue to work for some applications. This is why the audio widget always has a used memory value. Wifi is the same way.