Honestech FOTOBOX Plus - Manual (Page 88)

88. honesteh
Depending on the length of the music file and slide, it is possible that
the background music file may play underneath several slides.
Each additional music file that is added to a slide in the Storyboard will
be represented by a different color in the Music Track.
Note: Adding a music file to a slide that already has music beneath it,
will cause that background music to be overwritten by the newest file
being added.