This, sans the taunting. Taunting doesn't have any really affect. He will randomly "Delete" a player if someone has run through a color that is not their own.
I've tried the taunting method before, taunting about .5 second before his shield drops so that I still have his aggro forced for 5 more seconds, he usually does Deletion within 3 after the shield drops and regardless of whether or not his Aggro is forced on myself or the other tank.
You taunt too soon. The boss resets aggro a couple of seconds after the shield finishes the channel regardless of taunt. That's when you should taunt.