10.10.3 broke the dual monitor mode again on the 2010 Mini
On 10.10.1 dual monitors only worked if you unplugged the display port cable, then plugged it back in. You may have had to turn the corresponding monitor off, then on again too. Sleep would make the monitor strobe distorted graphics and you'd have to repeat the above process.
10.10.2 fixed all that.
10.10.3 broke it all over again.