gnome-applets-mixer-2.22.0-alt1.1

I have three volume applets (Master, Headphones, and PCM). Very often when I
change the volume level by scrolling the mouse wheel on the applet (Master), the
volume level changes indeed, but the icon doesn't change.
Steps to Reproduce:
1. start some sound (playing music; in order to observe volume level changes)
2. move the mouse pointer over the applet (Master)
3. scroll the mouse wheel
Actual Results:  
the volume changes, but the icon doesn't change.
(Workaround: move to another applet (e.g., Headphones), and change its volume
level. On that change the first applet (Master) also starts displaying the
correct icon.)