Low Priority Queue

My friend invited me to play a ranked game with him. So i joined his lobby and he said that he had a 20 min ban, so we waited the remaining 15 minutes in the lobby. He said that he got the ban because he left a match 'cause he had to do something. Now, after the ban was lifted we went into a ranked queue. There it said that we've been placed into low priority queue because my friend left that game and another one some time before that match. We eventually got into a match and ended up winning it. After this my friend logged out and i kept playing. I noticed that when i started searching for another game (normal this time) i had the red exclamation mark next to my queue timer and it said that i was placed into low priority queues. I haven't left a match in a while and i didn't have it before i played with my friend. Does anyone know what might have caused this, and if you do please tell me. Or was this just a bug?
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