Hotkey for play (ctrl + P) not working properly

Sometimes when I click ctrl + P it plays the scene sometimes it doesn't. I tried to click on different places in order for it to run, for example over the game window, somewhere around the play button but sometimes it works sometimes it doesn't. Even when I have already clicked on play with the mouse and then immediatelly, without commiting any other action, use the hotkey, it doesn't want to stop. All of this happens until I restart unity. Once I restart it it works fine again. What am I doing wrong?