Yosemite on 4K tv, now got monitor resolution locked at 1080p

[alemail]

I upgraded to 10.10 from 10.9.2 where monitor worked in hdmi 1.4 full resolution (3840) with my 4K Samsung 55HU7500. Now, I see capability limited to 1080p. This is only for MAC screen and desktop,
because the 4k film I can see at full res. As is clearly see, it's just the desktop YOSEMITE who has this limit. Any idea?

best regards from Rome Italy!

GA Z87 MX D3H + i7 HD 4600 as GPU

 

[truefaith]

Same problem here. It used to work just fine on Maveriks, with a Dell 28" uhd, hidipi, now it does not anymore (highest resolution i get is now 1080p) on Yosemite. Really sounds like Apple wants us to buy a new mac mini to use 4K, even if the previous one if perfectly capable of handling the uhd resolution.

 

[fannta1]

I just bought dell up2414q with new motherboard asus z97x-a thinking that I will just install yosemite and hidpi mode will work out of box... Such a nice dream, now i even tried mavericks but cant get it work with hidpi just like in yosemite. Dont kniw what to do.