Game Mechanics: a willowisp despawning during fight

[Nuker]

Second time this has happened now. I am pulling willowsips and a-willow-wisps to the freeport zone line in east commons. First time it happened it poofed as soon as i started punching it. This current despawn occurred after it started to flee.

The loc where this occurs is approximately 158, -1531, -50

not sure what other info is needed but my character name is Pank

Thanks