Custom Serializers - Unexpected preamble in read ByteBuffer?

[Chris C.]

I have a custom Serializer implementation that returns a ByteBuffer of 51 bytes during the serialize method; however, I notice when the ByteBuffer is passed into the read method on the Serializer when its fetched, I get 91 bytes, where I need to effectively skip the first 40 bytes of the buffer to read the data I had originally serialized.

Perhaps I have missed a detail in the documentation, but everything I have read thus far seems to indicate that if I return 51 bytes from serialize to EhCache that the read method will also provide me a buffer with 51 bytes.  

Why is there a difference?