cant go fullscreen with 1440p res on 4k display

[vanilla.t]

i have a 4k tv and im trying to use 1440p in full screen but the game wont let me, if i choose 1440p it shrinks the game and doesnt fill up the entire screen. if i switch window mode to full screen the highest resolution i can choose is 1080p. this is with direct3d. using gtx 1080