i noticed this, too...
i only have my jabra stereo headphones laying around right now:
Jabra C120s
and i seem to remember something about the LG VX9900 (enV) not playing stereo depending on the model of headphones being used...

I ordered some sennheiser MM50s, but they probably wont come till next week...
i should have access to another pair over the weekend; ill report back with my findings...

anyone else??