1. You are surely using the software renderer when the black box appears, right? It's a known limitation of the software renderer, it seems it's not able to make PNG tranparencies.
2. It's normal that it adds both files, one has all the music IIRC, the other has the definitions for the music to work <!-- s:) --><img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" /><!-- s:) -->.