This does not seem to be new on KT. You need to LoS the MC. I have done it a couple times on my hunter now and my pet holds it fine and it does not reset as long as I LoS the MC.
It is annoying on some other bosses though where growl simply does not work and the boss will reset if you FD. I have been able to work around most of them so far getting a kill on every raid boss through BT. I have not tried sunwell solo yet.