Meanwhile at Blizzard HQ...
Until Blizzard does something which actively provides an incentive for players to use the PTR for large scale raid testing, things like this will continue to happen. You'd hope Blizzard's internal QA would pick up on this shit but there's a lot of moving parts to a game as big as WoW. Not an excuse, per se, but it's an unenviable position to be in.