Alright, I'll try to do my best in describing how to recreate this. Unfortunally, I was unable to catch a screenshot or a replay due to client crash not long after.
1. Our team had the autobarrier / initative advantage.
2. Enemy summoned the snake, where it was quickly slaughtered.
3. After the enemy returning to the battlefield, Mei used barrier first (enemy team1), then Kazekage Gaara (enemy team2), resulting in a active sand/earth barrier.
4. When it was Mei's turn (enemy team1), she applied her 2 random ninja poison skill - which should only happen when Mei's barrier is active.