This is just a warning to others, we've just had to learn this the hard way.
We had to kill Beth'tilac on normal this week due to our lack of a second geared tank, finished off the instance clearing 6/7, everything on HC except Beth'tilac and rag won't spawn on HC for us.
Not seen anyone discussing it so I thought I would alert people of it just incase they're considering killing something on normal to get to rag quicker for that week.