I have read through all 35+ pages of replies of the monster thread started about this issue back in December 2013. It has since been locked, it seems, and I am unable to post my issues on that so I am forced to create a new post.
I have a Rev A03 version of the UP3214 (Bought March 2015) and although I do not suffer from the split screen issue when running MST mode at 60Hz, I do almost always still get the dreaded blank screen / no power when resuming from standby.
UP3214Q Rev A03 firmware
MSI GTX970 Gaming
Nvidia 344.75 drivers (latest as of this writing 4/19/2015)
I actually filed a case with nvidia on that. After a long while they got back to me saying they identified two separate issues - both the fault of the screen. One is not coming back on, the other is coming back on but with garbled picture (usually one half of the picture is garbled). And that they received a new firmware M1T104 from Dell which took care of the issue.