Sleep vs. Metamorph Bug

4v4.

My Dreadlord sleeps a Metamorphed Demon Hunter towards the end of metamorphosis. As MM ends, sleep appears to autorecast on the Demon Hunter but has no effect and he runs away. As hes running, I manually cast Sleep on him two different times and he continues to run. The spell animation goes off, the “Zzz” appears over his head, but he just keeps running.