Has any one been able to consume fast-path update PDUs in an RDP client?

I'm working on an RDP client with a friend as a pet project and we're trying to get fast-path updates to work since rdesktop hasn't supported this so far. We're able to process around 20-21 fast-path PDUs after the handshake before decrypti开发者_Go百科on starts failing. This is because somewhere in there, the RDP server is encrypting 20 bytes and throwing off the RC4 keystream. If I consume 20 bytes from the client decryption keystream at the right time and place, all my fast-path updates are able to be decrypted. Unfortunately, this "right time and place" changes depending on the sequence of packets the RDP server is sending.

I was wondering 2 things:

1. Has anyone been able to successfully get fast-path updates working in their RDP client, open source or otherwise? Obviously, MSTSC doesn't count :-)
2. Has anyone seen this issue with the 20 bytes or know of any reason why it occurs?

Any help would be much appreciated.