I reported this bug to my distro (Debian) and the following is mostly a re-paste of that bug report.

After upgrading some packages KMix now has two volume sliders in popup shown when
clicking the tray icon. I tried backing up the kmix config files in
"~/.kde/share/config" and deleting the old ones with no success. Please see the
following link for a screenshot:

http://imgur.com/OU9jy

I have found this bug is only triggers when something
other than the "Event Sounds" Slider is listed first in "Playback
Streams". So to reproduce:

1. Play an audio source with whatever program you wish (leave it playing).
2. Close KMix
3. Reopen KMix
4. Click the tray icon and there should be two mixers displayed in the popup
Kitty

Reproducible: Always




-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'stable'), (400, 'unstable'), (300, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 3.2.0-2-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages kmix depends on:
ii  kde-runtime              4:4.8.4-1
ii  libasound2               1.0.25-3
ii  libc6                    2.13-33
ii  libkdecore5              4:4.8.3-2
ii  libkdeui5                4:4.8.3-2
ii  libphonon4               4:4.6.0.0-2
ii  libplasma3               4:4.8.3-2
ii  libpulse-mainloop-glib0  2.0-3
ii  libpulse0                2.0-3
ii  libqt4-dbus              4:4.8.2-1
ii  libqt4-xml               4:4.8.2-1
ii  libqtcore4               4:4.8.2-1
ii  libqtgui4                4:4.8.2-1
ii  libsolid4                4:4.8.3-2
ii  libstdc++6               4.7.0-8
ii  phonon                   4:4.6.0.0-2

kmix recommends no packages.

kmix suggests no packages.

-- no debconf information