In the Material enum the SOUL_FIRE is specified as returning the BlockData class Fire. At runtime it returns an instance of CraftBlockData.
The returned instance is correct and Material not, because SOUL_FIRE (in contrast to FIRE) has no block properties at all.

The enum element SOUL_TORCH is specified as returning Lightable. At runtime there is an instance of CraftBlockData returned.
The returned instance is correct, since SOUL_TORCH (like TORCH) is not lightable.

I've created PR 955 in CB to help find such issues in the future.