Possible rank system bug

Last night I was at 89LP in Silver 5 and played a ranked game which I won. After the game I was notified that I qualified for a promotion series. I played the first game of the series after playing a few normal games and ended up losing. I played one more normal game then went to bed afterwards and this morning I realized I was back down at 85LP. I didn't play the last two games of the series, instead it immediately took away 15LP after the first game of the series.

I have no idea if this has been an issue in the past or if anyone else has had this happen but it's extremely frustrating. I've never played much ranked so if this is just a rule (as in, losing the first game of the series automatically loses the series) please let me know. Otherwise I'd like to know if there's a way to fix this.