MadMonk, on 11 February 2013 - 08:28 PM, said:
He is in fact correct. The game somehow thinks the boss is casting the Devouring Plague which causes him to get all the heals from DP. We had him heal over 40% once when he CCed both our shadow priests at the same time.
Just make sure that your shadow priests use devouring plague just before the boss uses his convert, that solved the problem for us.
Can you show logs with this? Seems pretty interesting...