In section 184.108.40.206 Receiving an SMB2 WRITE Request of the MS-SMB2 documentation it says the following:
"If the server implements the SMB 3.02 dialect, SMB2_WRITEFLAG_WRITE_THROUGH is set in the Flags field of the request, SMB2_WRITEFLAG_UNBUFFERED is not set in the Flags field of the request, and Open.CreateOptions doesn't include the FILE_NO_INTERMEDIATE_BUFFERING bit, the server MUST fail the request with STATUS_INVALID_PARAMETER."
SMB2_WRITEFLAG_UNBUFFERED should be SMB2_WRITEFLAG_WRITE_
I emailed Tom Talpey at Microsoft about this. He confirmed it was an error/typo and cc'd the firstname.lastname@example.org people. They emailed me and let me know the update will appear in a future release of the MS-SMB2 document.