I spoke with the seller (official DJI one) and they said that the button can come off but shouldnt. They suggested pushing hard down on it to "click" it into position, but as this is a 5D (ie pushing is a function of the button and I dont want to damage it. I've decided to push moderately hard and just be very careful when storing. Fortunately its not come of as yet but if it does and I lose it then it will go back. Just didnt want to lose the controller for 4 weeks as I'm having way too much fun as it is
GREAT DRONE!!