[mdpye]

There are certain conventions on instrument location which are very rarely broken. Drum kits are an easy example to examine, almost always panned so that the individual pieces match their positions relative to the drummer: for a right handed kit setup, hi-hit usually to the left of centre, ride cymbal to the right, toms high-low left-right. Another comment mentions orchestral layout for classical music. You would probably notice something was different even on pieces you'd never heard before. I'd find it pretty disconcerting, or mistake it for a deliberate departure on the part of the producer. But then I don't have any symmetrical headphones, so it's never been a problem.