Xfce sound volume problem

[IdolIcon]

Xfce version here.

I unlock the line out volume setting in order to set different volumes in each stereo channel (and I leave it locked again). As soon as I change the volume with the 'pulse audio plugin', the setting go back again to the same volume in both channels (even if they are locked). The same happens when I restart the system: Both channels always go back to the same volume.

I need to keep a different volume level for each channel. How can I solve this problem? Thanks in advanced.