Continuity mistake: When Ursula is filming Elton outside his old house, the digital camera produces a distorted picture and has four white lines in the corners. But, after Elton's flashback, Ursula is still filming but the picture is straight and the lines are gone. (00:04:40)
Continuity mistake: Jackie gets Elton to take his shirt off by deliberately making a huge red wine stain on the front. When Elton comes back to the estate with the pizza, his shirt is unstained. (00:27:17)
Continuity mistake: When the Doctor first appears in the episode, baiting the Hoix with a piece of raw meat, the meat turns around in his hand between the close-up and the wide shot. (00:02:30)
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.