Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.86
3 Screens (2 UHD via 2 hdmi slots and 1 FHD via display port slot)
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: rB26bd5ebd42e3
Short description of error
When I put the render window on the Full HD screen, and the main blender window is on the 4K screen, the UI glitches, the top menu goes off screen, I have to double click twice on title bar for things to go back to normal. Also, the window bar of the render window (with the blender name, and the reduce, maximize and close buttons) is too big. I'm guessing DPI issue between blender and windows. Blender's DPI appears correct.
Exact steps for others to reproduce the error
Put the render window on a seperate monitor, with a different resolution than the "main" monitor. Hit render.
Put the window back on the main screen, everything is fine.