I have two soundcards. For each one I have a mixer on my panel. Upon entering the XFCE Environment, both mixers have the same volume. It is the second mixer that copies the volume of my first soundcard. 

If I rightclick on the second icon, the true volume is displayed. When I alter volume in e.g. alsamixer, nothing happens.

Note: The copied value is only what xfce-mixer says:
If soundcard1 has master volume 80%, then the mixer2 says soundcard2 also has 80%. The real volume could be anything (unless it really has the same value)