Negotiating RemoteFX with a non-rdp 8 capable client

I am trying to connect a non-microsoft RDP 7.1 compatible client to a Windows 2012 SessionHost server.  The server has RemoteFX enabled and a Windows 8 Remote Destkop client works perfectly well. The non-Microsoft client works fine with

• Windows 7 VMs under Hyper-V
• Windows 2008 R2 SPI SessionHost
• Windows 8 VMs under Hyper-V (2012 Host)

but it will not receive RemoteFX updates from the server. The graphic updates appear to be fastpath bitmap updates, even though the client only negotiated RemoteFX as a codec in its capabilities in the Confirm Active pdu. It seems the server ignores this. Is there something else that must be negotiated with 2012?