[Client] Cannot select a champion for completing missions after a game.

I just started a new account because I live in a different server's area now. I've played about 5-10 games and after completing some quests the client asks me to choose a champion to unlock. There are three champions available that cover the entire screen. There's no "X" button or anything at the top even. When you mouse over the champions, there are two buttons that appear in the middle of the picture, one to look at the champion's abilities, and one to choose that champion.

The problem is that those buttons disappear when you aren't mousing over them. In my client, when I mouse over the area below them, they appear, but I cannot click on them because obviously my mouse isn't on them. Then when I try to move to click "choose this champion," the button disappears and I can't do anything. I can't queue up for another game, and I can't view anything normally available in the client. I've read a few other board posts that seem to have run into the same thing, but since there doesn't appear to be a fix yet, I figured I should post to and provide as much info as possible.

P.S. I'm posting here using my NA account, but this problem occurred on the Japanese server if that changes anything.