window won't stay up

When the window bounces back down as it is going up, often times it can be due to a restriction in the glass run or something impeding free movement of the glass to it's top most position. Since the window "thinks" an obstruction -- like an arm -- is in the way, it opens back up to prevent injury or damage. If this is not what you are experiencing, it could be that there is some concern with the switch or wiring that needs to be addressed.