On this line:

https://github.com/neo-project/neo/blob/master/neo/Network/Payloads/InvPayload.cs#L18

The InvPayload is specified as having two fields, one which is type and the other which is an arrayOfHashes. When I check the NEO network protocol documentation and the Bitcoin network protocol I believe there is a different implementation of this:

http://docs.neo.org/en-us/network/network-protocol.html

https://github.com/bitcoin/bitcoin/blob/5c2aff8d95a932f82a9472975b1d183da6c99e5f/src/protocol.cpp#L167

So what we have is:

Type, []Hashes

When docs say:

[Type, Hash]

With the current implementation, I think we are also restricted to sending only one InvType per Message.