Placed in Lower Priority Queue Over ONE Leave Game?

Then don't afk or leave.

50 isn't really a lot of games to go without leaving. It seems like the allowed range is somewhere in the neighborhood of 1 in 100. You weren't punished for leaving 1 game you just discard your history, but leaverbuster doesn't.

If you play enough games without leaving(again think about 100 per leaverbuster punishment) then your status with leaverbuster will improve and there will be a popup alerting you to that.