i get this problem, on my samsung 950 680 where fine, 780 sli this problem and coil whine. :( sad days

Yup the way MST works sending 2 streams over displayport seems to be causing your problems. That would explain your split screen problems.
I'm suprised latest Nvidia drivers haven't helped since this problem has been around for a while.
For example watch this video on a 4K monitor using displayport with Nvidia card they get major split screen problems, monitor going blank, having to reboot,etc. at 33:20 in this video which was over 6months ago!
http://www.youtube.com/watch?v=Wa-DRVqPJRo
 
Personally, I'm using my 460 cards with the Seiki 4K monitor and never seen any of the problems you mention or see in the video since I'm only using HDMI. Only downside is that you are stuck at 30Hz which isn't as big of a problem as people are making it out to be. Okay for my uses. Besides seems that there are still many more kinks to work out when you go to 60Hz as you found out and as you can see in all the video's I've seen covering 4K displayport. It's even worse if you are using AMD card too!
 
 

daviangel
Yup the way MST works sending 2 streams over displayport seems to be causing your problems. That would explain your split screen problems.
I'm suprised latest Nvidia drivers haven't helped since this problem has been around for a while.
For example watch this video on a 4K monitor using displayport with Nvidia card they get major split screen problems, monitor going blank, having to reboot,etc. at 33:20 in this video which was over 6months ago!
http://www.youtube.com/watch?v=Wa-DRVqPJRo
 
Personally, I'm using my 460 cards with the Seiki 4K monitor and never seen any of the problems you mention or see in the video since I'm only using HDMI. Only downside is that you are stuck at 30Hz which isn't as big of a problem as people are making it out to be. Okay for my uses. Besides seems that there are still many more kinks to work out when you go to 60Hz as you found out and as you can see in all the video's I've seen covering 4K displayport. It's even worse if you are using AMD card too!
 
 

This is due to fw issue on monitor and since this videoreview ASUS has relesed a new fw to fix the non boot MST issue so whats shown in the video is monitor fw issue, not driverissue since you say there is no difference with the latest one and i say it works when upgrading the monitor and i am only on the old 331.93 BETA but is was the same on 331.82 after the fw upgrade.
I have updated my PQ321QE with this new 1.02 fw and i can boot in MST, work in BIOS with MST Active and boot with MST Active.
You have to Contact ASUS for it so it is now up to DELL to bring out the same changes to their fw as nothing in the video is accurat anymore with all monitors shipped after a specific date as they come with the fw 1.02 from factory.
None of the issues they having i have and i can switch however i want, whenever i want and no boot requierd for it to work. No need for new fw specific for 4K to the titans either that some had to use to "fix" the fw issue.
I for now(might get super highend cabel later) just use the lockable DP-cabel that ASUS send with the monitor.

callsignvega
Don't use that mini-DP cable that Dell includes, that thing is really cheap. I have almost the exact same setup, 780 Ti Classified with the UP2414Q and don't have these issues. I do use a aftermarket higher quality cable though. 

Higher quality delivering digital? 

There is a long working thread on the Dell forum( ) where one of the moderators is asserting that there is an active dialog with NVidia on these issues.   Here is a brief description of what I am facing:
 
I have now had the Dell UP3214Q for about a month.
Problems:

1. Resume from Sleep - Monitor will not wake (tells me that there is no signal).  This occurs frequently, but not 100% of the time.  Requires rebooting everything to fix.  Turning monitor off / on, unplugging Display Port etc does not fix.  Bottom line is that I have to boot twice every time I start my machine...
2. Windows 8.1-64 Login Screen - always shows only half of the screen after a cold boot - shows both sides after warm boot (usually the right hand side).  I can CTRL+ALT+DEL, type my password (although I can't see my PW or account since it is clipped or on the non-visible LHS), Windows desktop loads and the monitor will go dark and usually (>90%) come up in the full 3840x2160x60hz mode.  Sometimes it does not and just goes dark... Have to follow the steps outlined in (1) to fix.
3. Resolution switches - Gaming - something that is a bit more rare, but similar in what bugs are surfacing - is that there are times that I exit a game and when I get back to Windows, the monitor goes dark indicating that there is no signal.  Again, power cycling everything is required. 

 
Other observations:

1. Of course none of this occurs in 30hz - which contrary to a previous poster is not at all acceptable for me. 
   
2. Other folks have tried a wide assortment of DP1.2 cables of differing qualities - no change in behavior
   
3. If it was a cable issue, I would not expect a specific pattern of actions from the software initialization perspective to make much of a difference...
   
4. It does seem that the dell monitor got the "Pre MST" boot stuff figured out, and that ASUS has fixed the issues that were specific to their mboards.  I always get a fine, non MST experience in bios mode... (when computer is booting and when I am in the BIOS).  This leads me to believe that it is more likely a video card issue.
   
5. Others that have different video cards, same monitor, have different experiences.  Ditto with AMD GPU's... different experiences.  (makes me think that this is less likely to be a monitor issue)
   

 
Questions:

1. I don't know or understand at what level in the software stack that the MST stuff kicks in - because it seems odd that I have the problem of half screen on Windows Login ...  Does anyone have a software stack model?  It would be great to get an idea of how this all works so I can know where to focus bug hunting efforts, although I suspect that there exist bugs in several different areas (Monitor FW, Graphics FW, Drivers etc). 
2. Are there different design approaches to how this problem is solved between AMD And Nvidia?  (I see lots of posts about how AMD handles this - not sure if it is better or not)
3. Is there anyone with this dell monitor, and the 780 [or other 700 series) and running in 60hz that has not had problems?

 
Facts:
OS: Windows 8.1 Pro 64bit.
SW: Dell Display Manager 1.20.0.1437
SW: NVIDIA Driver 331.65, through 332.21 - now will try 334.67 
HW: EVGA GeForce GTX 780 Hydro (3GB)
HW: Using the Dell-Supplied Display Port cable
HW: Asus ROG Maximus VI Formula (16 GB, 4770k)
 
I know that this is still a bit of a leading edge configuration (4k, 60hz in general) but I had assumed that there would be more stability after Sharp led the way a year ago or so... 
 
cheers.

AMD does not have this issue. Verified, tested.
 
But I'm having the same issue verbatim on UP3214q 32inch dell on titan gtx
 
upon cold boot , I get a half screen at windows login, reboot I get full screen
BIOS posts screen is fine on cold boot, "most" of the time
 
I have the latest titan bios that evga provided ( at least I hope its the latest)
 
EVGA Titan GTX, has issue on cold boot for windows login?
yes, I'm running dp 1.2, and have a high quality cable.
 
my system exceeds Dell's minimum spec
 
AMD cards do not display this issue with the up3214q 32inch dell, so then that means only two possibilities:
Is it NVIDIA driver issue, or is it NVIDIA bios issue
 
Where is support on this issue? Better bios? 4 titan gtx was rather expensive

JayVenturi
AMD does not have this issue. Verified, tested.
 
But I'm having the same issue verbatim on UP3214q 32inch dell on titan gtx
 
upon cold boot , I get a half screen at windows login, reboot I get full screen
BIOS posts screen is fine on cold boot, "most" of the time
 
I have the latest titan bios that evga provided ( at least I hope its the latest)
 
EVGA Titan GTX, has issue on cold boot for windows login?
yes, I'm running dp 1.2, and have a high quality cable.
 
my system exceeds Dell's minimum spec
 
AMD cards do not display this issue with the up3214q 32inch dell, so then that means only two possibilities:
Is it NVIDIA driver issue, or is it NVIDIA bios issue
 
Where is support on this issue? Better bios? 4 titan gtx was rather expensive

100% Wrong.  Many AMD cards also have the exact same issues with the Dell UP2414Q (and UP3214) monitors.
There is an updated A01 firmware available if you return your monitor to Dell.
Thread here: 
 

callsignvega
Don't use that mini-DP cable that Dell includes, that thing is really cheap. I have almost the exact same setup, 780 Ti Classified with the UP2414Q and don't have these issues. I do use a aftermarket higher quality cable though. 

It's not the cable.   There's a firmware fix for the monitor.  Maybe you have the updated "4k" nvidia bios that also helped with the issues?   Thread here: