Ana Sleep Thwarted by Overwatch Railing

When McCree pops his ultimate, the ears of every Ana player on the planet perk up. They have mere moments to whip around, spot the creeping cowboy, and launch their Sleep Dart into his solar plexus to save their team.
Sometimes, even that is not good enough. Sometimes the universe simply isn't on your side. Such is the case in this clip posted to the Overwatch subreddit Tuesday by u/Joey-__-.
Joey-__- and their team are contesting the cart in the tunnel before the last point on Numbani, fighting desperately to keep the game alive. As Ana, Joey-__- is positioned in the back line, healing their teammates from a safe distance.
All of a sudden, Joey-__- hears McCree's voice ring out from their left. They whip to the side and spot the cowboy on the balcony behind their team; in the same motion, they pull their dart gun and launch a dart straight at the McCree. The dart appears to hit McCree dead center, but no hit markers pop up. Instead, he activates his ultimate and kills both Joey-__- and a teammate.
A close-up review of the tape reveals the dart hit the thin railing right in front of McCree rather than its intended target, thwarting Joey-__-'s valiant attempt to save their team.