No Chest for S-?

First off, I posted this in bug-reports, because I thought it was a bug. Riot took it down and told me to post it here (kindly), but didn't tell me whether it was a bug. So, please help guys.

I just bought Katarina yesterday, and I just played a game with Katarina five minutes ago. I got an S- and didn't receive a chest. When I look at my champion screen (in the old client), and I highlight her, it says, "Season highest grade: S-," but she doesn't have the golden border, and her chest icon isn't highlighted.