Continuity mistake: After the Master changes all humans into copies of himself and Wilf says, "What have you done, you monster!?", it goes to all the different Masters in the room saying, "Are you talking to me?" The Abigail Naismith-Master is shorter than the Joshua Naismith-Master. In another shot they are the same height. The Abigail Naismith-Master is wearing very high heels and should be taller than the other Masters. (00:56:00 - 00:56:50)
Continuity mistake: After Lucy gets the bottle from the guard, as she explains to the Master that her family had contacts to create something to counteract the "potions of life" used to resurrect him, she starts to take the cork out of the bottle with her left hand, the camera cuts away to the Master and when it cuts back to Lucy, her left hand is on the bottom of the bottle, before she starts to take the cork out again. (00:15:00)
Continuity mistake: During the Doctor and the Master's conversation in the junkyard, the Master gets dust on the legs of his jeans. Just before he lightning-jumps away, the dust vanishes. (00:35:15)
Continuity mistake: After the Doctor and Wilf get off the seniors' bus, they're waving goodbye. In a close-up shot, the Doctor is waving with his right hand, but in a wider shot immediately afterwards, he's switched to his left hand. (00:25:10)
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.