Have you tested in scout to try and see what is happening?
The byte array will be being encoded into amf before transmission but it is a binary format and should be pretty efficient. I think the strangest thing is that it doesn't happen when wrapped in an object.
Does it happen outside of worker context i.e. if you try serialize it youself with a writeObject into another bytearray?
Hm maybe the decoding side or the transmission is the problem, sounds a bit like a bug too to me.