I'm using a MiniDP to DP cable and sometimes the external monitor just wouldn't get any signal after sleeping the laptop with the cable plugged in. Unplugging the cable or power cycling the monitor doesn't help at all. I have to completely restart the laptop to get a monitor signal again. I wonder if that's due to the pin 20 issue.
The funny thing is that I actually bought 4 different cables already and all of them have the same problem.