VB headphones acting strange?

I just recently bought the official Virtual Boy headphones (brand new) off of eBay. When I got them and tried them out with “regular” music, they sounded strange. It seems as if one side was bass and the other treble and the bass side is louder (I checked and I don’t think it’s the music). Is this normal? It’s not really noticeable on the Virtual Boy, but I want to make sure there’s nothing wrong before I leave feedback.