Buying a champion while in team builder bug-mordekaiser [Client]

I tried to buy mordekaiser while in teambuilder and it worked, but then after I got out of the game I played, i tried to use him and it said invalid_champion or something like that and he disappeared from my champion select. I had to waste one of my refunds to refund him just so I could buy him again. I also relogged many times during this process. [Client]