Mr Incredible :
So I take that i might be wrong but can you please explain to me how you use match bonus in champs and tournament matches? As far as i know it can only be used in matches that you physically start by challenging another team, like practice matches and guild challenges. When you start a game with match bonus on, they ask you when you start the match if you sure you want to spend XX amount on match bonus, if you click 'yes' the game starts. In tournaments and champs matches start automatically, you don't click to start them, i have had match bonus on already when i played tournaments and they definitely don't ask if you wanna use mb before the game starts or take the money for it, so don't see why you say it can be used in tourneys and champs, unless i missed something major in the game to this point.
In fact I just went to try it out now again and I'm unable to use match bonus in championship matches, I had mb on 20% but the tournament match started without them asking about mb or taking the amount it would cost from me so clearly it don't work. It only works at matches that you must click on 'play match' to start the game. Thats also why you can use it when you challenge opponent in guild challenge but its not used when they challenge you, cant use it when they challenging you because you not the 1 starting the match.
The money to pay for MB might not be taken out of your account immediately after a championship game but if you close the app and open it again it will be gone for sure.