I have a Dell UP2414Q 4K monitor. If I want to display 3840x2160 @ 60Hz, it uses the MST mode of DisplayPort 1.2 giving me two 1920x2160 tiles on the monitor. After a lot of poking around, I found that this is the expected behaviour. One solution is using Intel HD 4600 driver's collage mode, akin to AMD Eyefinity, except that it is extremely limited and this mode does not support spanning a subset of your monitors. So, you end up with windows thinking there are two portrait monitors beside each other as two separate monitors would look. This causes Windows Store apps only use half of the screen and when you maximise a window it will only maximise to half of the screen.
It is a workable solution if you consider screen split into two sides a feature, except for the fact that Windows 8.1 guess the DPI incorrectly, causing a resize of windows when moved onto the monitor. It is especially noticeable in IE 11 where the contents of the browser shrink significantly.
How does Windows guess what dpi setting should be used for a display? How do I convince Windows to use a different value?
Also, if you change the monitor to run in DisplayPort 1.1 using SST mode, it displays 3840x2160 @ 30Hz, and Windows correctly guesses the DPI setting of the monitor.