broken leaver buster?

i just experienced for the 3-rd or 4th time that i got back to matchmaking from champion select and got 5 min penalty before being able to matchmake again although i was still waiting for my turn to choose champ in champ select i think it was at least 3 enemy players till left to choose and those on my team....

wtf?! penalty for nothing ? broken ? only me who experienced this ? help ?