Have been having the same issue. It only happens when my game res is 1920*1080 (100% of my screen) and/or higher.[1] Bug disappears when i increase HDR quality from very low to low, but in this case most objects and ground will not even render.[2] Sun shines even through ground in the night.[3]

My specs:
Win 7 64-bit
AMD Radeon HD 6800 Series
Intel Core i5-2500K 3,30GHz
8GB RAM

GPU drivers up to date
GPU temperature totally ok
DayZ runs at 40–60 FPS with app. medium settings

[1] https://imagizer.imageshack.us/v2/1500x844q90/841/ta5a.png
[2] https://imagizer.imageshack.us/v2/1500x844q90/845/vwc4.png
[3] https://imagizer.imageshack.us/v2/1500x844q90/600/db7e.png