[Gameplay] Wrong Character Receives Rift Herald Buff

In a recent game, I was playing Nunu jungle and my teammate was playing Gnar top. We went for the Rift Herald. When his health was low, I left the pit and headed down towards my blue leaving Gnar to finish him off. When he landed the last hit, it appeared in chat that Gnar had slain the Rift Herald. I looked up to see whether the buffed minions were pushing top, and noticed that Gnar did not have the buff and that I had the buff instead. I will see if I am able to reproduce this bug. I have successfully passed the Herald's buff to other players many times, so there is likely something unique about why this happened. If it hadn't said in chat that Gnar had slain the Herald, I would have assumed that I killed it with a DOT.

Steps: 1.) Attack the Rift Herald with a partner 2.) Walk away from the pit when the Herald is low 3.) Let your teammate last-hit the Herald 4.) Receive Herald's buff

Possible additional steps: 1.) Play Nunu 2.) Smite Rift Herald 3.) Have your teammate become Megagnar right before last-hitting the Rift Herald