While I think this should be bug fixed (as other classes can easily do it), here's how I made it happen. Wait until the mobs spawn before the claw attack. Wait until you are at the last set of enemies. Pop your F3 virtue and get hit by an enemy. Your perpetual Aegis will be gone (or will be gone after 20 seconds instead of a perpetual timer) and while your virtue is recharging it won't pop back up.