This is a report for a teammate since he had to leave. He received a ban at the end of a game after the victory screen popped up and it was at least 10-15 seconds after. He clicked leave game and it gave him a 30 min leave ban. He had to leave anyway so it didn't affect him but, it might be an issue in the future for other people.
Might have been a bug, but it also might just be a need to allow players to leave after the victory or defeat screen rather than waiting 30 seconds for the game to close the server for us. Because I'd rather re-queue and use those extra 30 seconds to look for my next game than sit and look at a still screen for 30 seconds.