Noticed this issue just now. Whenever i minimize the game window when playing in a window, or when alt-tabbing while in fullscreen, in both these cases the GPU load jumps to 98-99% from whatever it was while actually playing (usually 45-65%).
This is clearly a bug, most other games tend to throttle down cpu+gpu usage when the application window loses focus.
Might be OS+hardware issue too, cannot test out on other systems right now, im travelling with laptop that has Win 8.1 64bit + nVidia gt750m graphics.
Early bird gets the worm, but second mouse gets the cheese.