Has this been confirmed? I have read no evidence at all that the cementing job that Halliburton performed that sealed the area between the outside of the casing and the borehole has failed. I have seen and participated in lots of discussion that cementing of the casing itself was deferred under direction by BP until the mud was removed from the casing. That just doesn't make sense to me at all; I don't care what pressure tests they ran. They had apparently experienced several pressure spikes leading up to the incident even when driller's mud was in place, so how could removing that mud have had any positive results?
Also, there have been several discussions about three plumes of oil and gas coming up; but although the investigation may determine otherwise, I suspect these plums came up through the blowout preventer piping. Remember that the blowout preventer had apparently been modified by BP, and reports were that drawings of the modifications may not even exist. This appears to be common when construction folks take the engineers' design and implement it. That may very well explain why attempts at activating the BOP didn't work. Perhaps they were operating the wrong valves? Nobody knows yet, but when they retrieve the BOP, it needs to be examined in the open by a group of proper experienced professional so that nothing can be hidden.
No, I've just heard the cementing comments said by a rig worker on the radio, so I wouldn't consider it gospel.
The BOP being inoperable seems to be confirmed, as it didn't close automatically, the people on the rig were unable to close it manually, and it clearly leaked. An operating BOP should have prevented both the explosion and some (at least) of the spill.