Cursed Blade bug when combined w/ Red Buff

Edit: May have to click the link to view externally at the timestamp, or go back in the embedded video by like 30-45 sec.

My theory:

Attacking enemy champions while Red Buff is damaging them prevents Cursed Blade from lowering their star level.

You can see their health go down, but they retain their same star level champ and their health goes right back to normal. Maybe has something to do with the way health is applied/reduced while red buff is active, not sure.