Hey there corndog!
From my watch of the video, it appears like the Void Prison just never hit the Illidan. Notice that the “Stopped” UI on his name plate never shows up, which is a good indicator that he wasn’t Stopped at any point during his wind-up for The Hunt. I think this might just be a good example of an ability missing and not any sort of bugged interaction.
Feel free to send us the replay following the instructions on this thread if you feel like my analysis is wrong after a second viewing, and I will open it up and look at what I see!
Thanks!
Huginncord