UltraHD Problem

Unity Engine
1

I encountered a problem where a Unity application sees a UltraHD display as 2560x1440.
I developed a dedicated project for that. On the first picture you can see an UltraHD full screen (3840x2160). Inside there is a test grid where clearly mmust be distinguished lines with width of one pixel. It is not so and the label says the screen is 2560x1440 and putting GUI.Label on the axes confirms that.

1887551--121450--1.png
1887551--121450--1.png3840×2160 93.4 KB
It causes problems in my current project which is aiming and high-end screens and it makes it impossible to design it well. It seems like whatever I do I cannot go over the 2560x1440 limit.
The system is Asus G751J with GeForce 980M 4GB. Running on Windows 8.1. Unity 4.6 Pro trial. The problem occurs with dual display. The laptop is HD 1920x1080 and the extension display is 3840x2160.
The display dialog in the beginning confirms the resolution of 3840x2160.

Is it a Unity bug that a UHD app cannot use all the pixels on screen.? If not how can I make my full-screen UHD example work and show precisely the pixels?

In Full HD (1920x1080) everything is good.

1887551--121451--6.png
1887551--121451--6.png715×663 27 KB

1887551--121452--4.png
1887551--121453--3.png
1887551--121453--3.png1920×1080 39.5 KB

2

The test project attached

1887552–121454–TestUltraHdBug.zip (1.55 MB)