Minimized game still taxing GPU??

While playing WOT I will minimize the game to browse and take a break at times. I usually always have temp monitoring software running and sometimes I notice that even while the game is minimized its still taxing the GPU. Runs at its max reached temp while gaming even when minimized???

It dont happen all the time and when it does I can open it and re minimize the game and it cools down like it should.

Normal? Whats causing this?