If someone you partied with last (ever?) joins game a game, you get booted

[winnix830]

I've had this happen twice. Both times I wasn't partied with anyone and was a fair bit into a game. The first time, the last person I partied with independently joined the queue and mid-game I got the select hero page. This time, the last person I partied with started a game and I was returned to the hideout despite being mid-game. (match ID for the recent one if that's helpful: 53104818)