There have been some bugs noted in Black wing later, that will be addressed in future updates.Here is what Blizzard has to say about the bugs:

We want to formally address player concerns regarding issues found in Blackwing Lair. Blackwing Lair is currently the highest tier raid dungeon in the game, designed to be a very challenging encounter for even the most powerful guilds to defeat. Since its launch, we have discovered some key issues which are making Blackwing encounters easier than intended. This applies to both Razorgore and Vaelastraz encounters. One related issue is also preventing the door to open after Vaelastrasz dies, not allowing players to advance beyond the Vaelastrasz the Corrupted encounter. While this is a bug, players currently should not be able to progress beyond the Vaelastraz encounter by any means, and anyone found in areas beyond the second door will be considered to be exploiting the game.
Through game updates, we are addressing these issues to make sure that all the encounters in Blackwing are working as intended, and that players are able to progress through the dungeon. We will provide further updates throughout the week as they become available.

You can disscus the bugs here.