Unable to use 3840x2160 resolution with SLI

I have two EVGA GTX 980 Ti Hydro Copper with a Samsung U28E590D (UHD/4K) monitor connected using DisplayPort.
Whenever I enable SLI on my graphics cards (Option “SLI” “Auto”), the 3840x2160 resolution simply disappears from xrandr and nvidia-settings, and the highest selectable resolution is 2560x1440. Not even 3840x2160 at 30 Hz is available.
Is this a known issue? I can’t seem to find any information about it at all.

I am using Linux 4.2.3 with NVIDIA driver 361.28. I have tried setting “PreferredMode” in my xorg.conf, to no avail.
SLI works just fine with 3840x2160 on Windows.