RE: UP3214Q - no picture after powering off the device / half picture at the login screen
At least over here the screen is backordered so I'm still waiting for my replacement.
I never had cable issues but that may stem from using the cable that came with the U3014 - though the product code seems to match the cable that came with the 32"er.
@E.T. you seem to be the only one with an ATI setup - do you have any no picture issues after a display power off and on if the PC stays on?
The weird resolutions IMHO are due to the tiling. In DP 1.1 mode you can (by defining custom resolutions in the nvidia cp) create proper 16:9 resolutions, something which doesn't work in DP1.2 (either due to the hardware not supporting it, or driver issues). If you look at the resolutions your display reports to windows, they seem to be mostly lower versions of what one tile (screen half) can do.
I'm hoping that the influx of cheaper 4K screens will force hardware and software makers to make this setup more reliable as right now it seem hit and mostly miss