Is it a by-design behavior that MessageContext.Items are flushed in the DeserializerConsumerMiddleware middleware?

[Fram90]

Hello.
My idea is to save raw byte[] message in items before deserialization, I need it further for my logic. But when I save it to MessageContext.Items it disappears after DeserializerMiddleware handles the message.
As far as I understood from the source code, DeserializerConsumerMiddleware invokes SetMessage method that flushes Items collection.
In my opinion it is quite a confusing behavior. As a user I expect that during message handling process message context should be the same along all middlewares, since the message is the same, deserialized or not.
Could you please give some clarification on this subject, whether it is a bug, or a by-design behavior?
Thanks.