It works correctly on my setup.
Monitor = UP2414Q
Video card = Asus GTX760 CU2 2GB
Cable = Dell mDP to DP
Computer = i7 CPU, 32GB
Operating System = Windows 8.1 64bit (latest drivers, bios etc.)
Display set to 3840x2160 - DP 1.2
Another Dell 2413hm connected via MSI GD80 HDMI. I had issues in December, not sure if this was solved or not, but I haven't gotten around to connecting both monitors to GTX.