If an instrument is put through a digital delay with unequal delay times for the right and left channels, it will sound like it's coming from both speakers but not the phantom center. Reverb, chorusing, and other types of processing can also have the same effect. This is an intentional artistic decision of the person who mixed the music. If everything else is imaging as you think it should, I wouldn't worry about it.

[This message has been edited by soundhound (edited December 29, 2002).]