I've been follwing this thread because I have the same issue with one of my Windows 7 masters. Update the agent to 5.1 or 5.1.1 and it drops the PCoIP connection but it works fine using the 5.0.1 agent. For now I've just rolled back to the 5.0.1 agent on that master image. It'll take me a while to redo the image from scratch if that's the only solution, as it's our main lab image that involves a lot of software installs and tweeks. What a pain when it works fine with 5.0.1, not sure what changed.
Other Windows 7 images that I have in our environment updated fine to 5.1 or 5.1.1.