percussion mp3 export is all piano?!?

So I'm working on a marching band percussion score. When I try to export an mp3 of individual parts, it comes out as piano. Doesn't matter if its a marching snare, tenor, bass, or Marimba, Vibe, Xylo. EVERYTHING is piano. What's also weird is, even thou its an individual part, it sounds like all the parts are coming out... as piano! This has never happened to me before. It sounds REALLY cool, but obviously not what I want.

The only problem I can think of is that I wrote the score with v 3.0, and am now using the latest 3.1. I've never had any issues editing, or with playback thou.

If anyone knows what the problem might be, I'll be forever grateful! Thanks!