Ranked seires bug

Up front sry for bad eng, now to the problem. So i had a pretty good victory streak and i got in to promotion for s2 and first game in my promos i lose and it seas i failed my promos, now as i remeber in promos in the same league u need 2 win so it's ok to have 1 lose and 3 wins if ur going in the next league, like from silver to gold. So did they change that or is this a bug...?