I completely blame this whole incident on Blizzard.
Was there a bug? Yes.
Did Ensidia discover the bug? Yes.
Did they stop their attempt? No.
Why not? Because they have limited attempts and they are the top guild in the world trying for a world first.
If the fight had been tested on the PTR there would have been no fault. That is Blizzard's fault.
Does Blizzard really expect Ensidia, in the adrenalin of the moment, when they have been grinding the instance and have downed Putricide, Lana'thel and Sindragosa strictly and carefully to still have enough attempts on the Lich King on the first night the fight is available, to just wipe it and talk to a GM about a possible bug, when there is no guarantee how long the GM will take to get back to them, and when there is no guarantee they will have their attempt refunded? Pfff Not a chance.
Ensidia have a reputation to uphold (and it is a very good reputation that makes a lot of people jealous). They would never try a deliberate exploit. Were they reckless as to whether there was a bug or not? Clearly they were. But what do you expect? They were trying for a World First!