[PvP] League - won game, lost pip
If you disconnect from a match, for any reason, and do not return to it within the grace period (somewhere between 30 seconds to a minute), you will lose pips regardless of whether your team won or lost.
Not a bug. This is intentional design to discourage people from leaving matches or playing when their connection is unstable. Please remember that there are 9 other players in the match with you, and whether you are active in the match impacts their enjoyment.