For 2 years, I used a Cintiq 21UX as the main monitor with a 2009 Mac Mini. It was connected with a mini displayport to DVI-I adapter and worked perfectly.
I replaced the Mac with a new i7 with the same setup (the mini displayport plugs into the thunderbolt port). When I boot the system or wake it from sleep, the image does not appear on the screen. The Cintiq's status light turns blue for a few second (its ON setting) then turns amber (its SLEEP setting). I have to unplug it and plug it back in to get the image to display.
I updated to the latest Wacom driver, reset the PRAM and SMC, but the problem persists.
I got a new MDP to DVI-I adapter and it works fine. I don't know why the Startech adapter worked with the 2009 mini but not with the 2011. Startech tried to sell me a much more expensive active adapter, but I think that's unnecessary and even the Apple adapter is passive.