Toggling mute (via my ThinkPad's hardware mute button, 'm' when Master is
selected in alsamixer, or 'amixer set Master toggle') mutes both Master and
Speaker, but unmuting (by any of the above three methodes) only unmutes Master,
and Speaker must be unmuted separately.

I recently upgraded from Wheezy to Jessie - the problem was not present before
the upgrade.