The Sport audio decoding is handled by a third party, so it is very, very unlikely that Sandisk is going to fix any compatibility issues you find at this point.
The other thing is taht depending on how the Vorbis files are encoded, it may not even be possible to play them on simple devices like the Sport (which has a tiny amount of RAM). The Vorbis spec defines no upper bound on how much memory can be required to play files. It is certainly possible to make files that will fail on anything less than a smartphone/PC, and probably not very hard for devices like the sport that have only tiny amounts of RAM.
