Continuity mistake: After Korwin cuts the power to the stasis pod, close-ups of the Doctor inside the pod show light still on in the pod. A shot from outside the pod, however, after McDonnell runs off to deal with Korwin, shows the inside as being dark. (00:35:25)
Continuity mistake: When the Doctor asks Captain McDonnell how many other crewmembers there are on board, he grabs her arms. After she tells him "three", the Doctor lets go of her as Scannell explains that the ship transports cargo across the galaxy. In the next shot, facing the Doctor, he's holding McDonnell's arms again. (00:03:00)
Continuity mistake: When the Doctor starts scanning Korwin, he's holding the sonic screwdriver with his thumb on the end without the light. When Ashton says that Korwin sabotaged the ship, the Doctor's grip on the screwdriver has changed to one without his thumb on the end. Shortly after, he has his thumb on the end again. (00:06:10)
Continuity mistake: When the Doctor comes up with the idea of using the generator to restart the ship's engines, in a close-up he's gesturing with his right hand, but in a wide shot is gesturing with his left. (00:10:15)
Continuity mistake: After McDonnell warns the crew that the possessed Korwin killed Abi, Ashton orders Erina to hurry up with the equipment she was sent to fetch, and she mutes the com before removing several pieces of equipment from a locker, holding them with her right hand and arm. When she closes the locker door, revealing Korwin, the equipment disappears. (00:15:20)
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.