Not sure if everyone is aware, but there is a tool your supposed to use in the combination valve when you bleed your brakes. It's purpose is to keep the pressure differential valve from moving to the front or rear when bleeding. Seems the issue some are having may be because this valve moved during bleeding and will not re-center on it's own, you have to manually do it.
A little video of the tool
https://www.youtube.com/watch?v=osC7t3s3J7g
A nice video of how a combo valve works and also the tool
https://www.youtube.com/watch?v=qPLaPv8DITE
Also some good troubleshooting guides from CPP
http://www.classicperform.com/TechBo...t.htm#testprop
Another:
http://www.mpbrakes.com/techtalk/how...ing-brake-drag
I don't think this one is a CPP issue or a bad combo valve (this same thing happened to me and it was the PDV had moved), but they should have known how to re-center the valve and offered proper bleeding instructions using the tool.