FOST Removes Deathmark?

I haven't tried this in any of the raids yet but I've noticed that when FOST does his team buff and Advantage up ability it removes the Deathmark left by Mace Windu in the tank challenge. This might be a glitch but I read the discription and it doesn't mention removing debuffs and yet he has done so at least 10 times for me. It's cool and it might make this toon viable if it actually worked like that and the disruption gets changed to actually remove debuffs normally.