Alienware (Nvidia) + 2 monitor on ubuntu 14.04 (1 of the displays does not show)

Question

I just installed a clean Ubuntu 14.04 on my Alienware laptop as dual-boot (The problem does not exists on Windows 8).
I change the driver to the nvidia (GeForce GTX 860M) one through the additional drivers tab.
I then added two monitors (1 to hdmi + 1 to mini display port)
The problem now is that if I have more than 2 screens on, the 3rd one (The laptop's own in this case) behaves like a corrupted signal and if I go to the x server configuration, I only see one display (no matter how many displays are on).
Does anyone know why this happens and/or how to fix it?

Note: It used to work like a month ago. I'm not sure if there was an update for the driver, but it stopped working from one day to the next.

xrandr:

Screen 0: minimum 8 x 8, current 3840 x 1080, maximum 16384 x 16384
DP-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 509mm x 286mm panning 3840x1080+0+0
   1920x1080      60.0*+   59.9     50.0     60.1     60.0     50.0  
   1280x1024      75.0     60.0  
   1280x720       60.0     59.9     50.0  
   1152x864       75.0  
   1024x768       75.0     60.0  
   800x600        75.0     60.3  
   720x576        50.0     50.1  
   720x480        59.9     60.1  
   640x480        75.0     59.9     59.9  
DP-1 disconnected (normal left inverted right x axis y axis)
eDP1 connected (normal left inverted right x axis y axis)
   1600x900       60.1 +
   1440x900       59.9  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 509mm x 286mm
   1920x1080      60.0*+   50.0     59.9  
   1920x1080i     60.1     50.0     60.0  
   1280x1024      75.0     60.0  
   1152x864       75.0  
   1280x720       60.0     50.0     59.9  
   1440x576i      50.1  
   1024x768       75.1     60.0  
   1440x480i      60.1     60.1  
   800x600        75.0     60.3  
   720x576        50.0  
   720x480        60.0     59.9  
   640x480        75.0     60.0     59.9  
   720x400        70.1  
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
  1024x768 (0x2d4)   65.0MHz
        h: width  1024 start 1048 end 1184 total 1344 skew    0 clock   48.4KHz
        v: height  768 start  771 end  777 total  806           clock   60.0Hz
  800x600 (0x2d5)   40.0MHz
        h: width   800 start  840 end  968 total 1056 skew    0 clock   37.9KHz
        v: height  600 start  601 end  605 total  628           clock   60.3Hz
  640x480 (0x2d7)   25.2MHz
        h: width   640 start  656 end  752 total  800 skew    0 clock   31.5KHz
        v: height  480 start  490 end  492 total  525           clock   59.9Hz
  1920x1080 (0x2d8)  148.5MHz
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock   67.5KHz
        v: height 1080 start 1084 end 1089 total 1125           clock   60.0Hz
  1920x1080 (0x2d9)  148.5MHz
        h: width  1920 start 2448 end 2492 total 2640 skew    0 clock   56.2KHz
        v: height 1080 start 1084 end 1089 total 1125           clock   50.0Hz
  1280x1024 (0x2de)  135.0MHz
        h: width  1280 start 1296 end 1440 total 1688 skew    0 clock   80.0KHz
        v: height 1024 start 1025 end 1028 total 1066           clock   75.0Hz
  1280x1024 (0x2df)  108.0MHz
        h: width  1280 start 1328 end 1440 total 1688 skew    0 clock   64.0KHz
        v: height 1024 start 1025 end 1028 total 1066           clock   60.0Hz
  1152x864 (0x2e0)  108.0MHz
        h: width  1152 start 1216 end 1344 total 1600 skew    0 clock   67.5KHz
        v: height  864 start  865 end  868 total  900           clock   75.0Hz
  1280x720 (0x2e1)   74.2MHz
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock   45.0KHz
        v: height  720 start  725 end  730 total  750           clock   60.0Hz
  1280x720 (0x2e2)   74.2MHz
        h: width  1280 start 1720 end 1760 total 1980 skew    0 clock   37.5KHz
        v: height  720 start  725 end  730 total  750           clock   50.0Hz
  800x600 (0x2e8)   49.5MHz
        h: width   800 start  816 end  896 total 1056 skew    0 clock   46.9KHz
        v: height  600 start  601 end  604 total  625           clock   75.0Hz
  720x576 (0x2e9)   27.0MHz
        h: width   720 start  732 end  796 total  864 skew    0 clock   31.2KHz
        v: height  576 start  581 end  586 total  625           clock   50.0Hz
  720x480 (0x2eb)   27.0MHz
        h: width   720 start  736 end  798 total  858 skew    0 clock   31.5KHz
        v: height  480 start  489 end  495 total  525           clock   59.9Hz
  640x480 (0x2ec)   31.5MHz
        h: width   640 start  656 end  720 total  840 skew    0 clock   37.5KHz
        v: height  480 start  481 end  484 total  500           clock   75.0Hz

Answer 1

Why you see only one screen in X is because 1920*2=3840. (X makes it one huge screen)

Why the laptop is showing a distorted signal is theoretically (=according to specs) because you use the mini-display port. 2 external monitors are only supported on HDMI and VGA.

Fair warning: I don't have your exact hardware, so borrow a VGA cable before you buy one to test this yourself (and before you accept my answer)...

Edit:

The standard Ubuntu NVidia drivers generate some problems on slightly older and slightly newer NVidia hardware.

If you want more then the standard Ubuntu repository drivers, install the xorg.edgers PPA. As the xorg.edgers group ask not to give installation instructions directly without linking to their page, this is the best I can do.

If you don't know what a PPA is or need some guidance after reading their page, leave a comment below.