BUG? Mix_VolumeMusic doesn't work on linux

I was playing around and found out that on linux, if you are playing a wav file as your music, and then try to:

Mix_VolumeMusic(MIX_MAX_VOLUME/4);

It will not affect the volume level, while if you have other types (for instance mod), that same command will modify the volume level.

Any ideas/workarounds? is it just my system (Suse 8.1)

Thanks,
Jesse