Finding with a Buffer returns null

[gdw2]

The following over-simplified code shows how I'm trying to use a Buffer as a key (a sha256 hash in this case). When trying to find a document based on the buffer, I always get a null doc in return. This does work when I switch from tungus to mongoose (i.e. mongodb).

MySchema = new Schema( key: type: Buffer )

Integrity.findOne(key: someKey, (err, doc) ->
  # doc is always null with tingo.  Not so with mongodb.
)