As you can see in the video if you start the game and go to another window when the game finishes loading the mouse is stuck in the upper left corner. It's not today that this happens but it's been annoying when you have to start/close the game several times because of modding.
If you click to play and wait for the game to open/load in its window, it doesn't happen, but being honest, most click play and go to another window when the game loads.