I am using MB4 for flash and MB5 for another summoner spell (those are the next/last page buttons on your mouse, if it has those). Now since the new launcher is there it sometimes tabs me out of the game, when I use summoner spells. This is of course very annoying, as flash for example sometimes works as your last escape tool i.e. and then closes the game. It does not occur on a regular basis tho. As soon as it tabs me out once, it does not happen again for the next few times.