Could anyone use a fast path PDU in an RDP client?

Question

I am working on an RDP client with a friend as a pet project, and we are trying to get updates for quick access, since rdesktop does not yet support this. We can process about 20-21 PDUs with high speed after a handshake before decryption will fail. This is due to the fact that somewhere there the RDP server encrypts 20 bytes and throws out the RC4 key. If I use 20 bytes from client decryption caching at the right time and anywhere, all my quick updates can be decrypted. Unfortunately, this “correct time and place” varies depending on the sequence of packets sent by the RDP server.

I was interested in 2 things:

• Has anyone been able to successfully get open-source fast-track updates that work in their RDP client or otherwise? Obviously, MSTSC does not take into account :-)
• Has anyone seen this problem with 20 bytes or knew why it occurs?

Any help would be greatly appreciated.