Continuity mistake: Martha reaches her right hand up to open the window, prompting Julia to panic and say "Don't! We'll lose all the air!" When the shot changes as Martha points out that the windows aren't exactly airtight, her right hand is suddenly lowered. (00:09:47)
Continuity mistake: When Martha is walking up to the hospital just before the motorcycle gear-clad slab bumps into her, her right hand goes from by her side to holding her purse strap between shots. (00:02:15)
Continuity mistake: When the Doctor puts his tie back on after returning from the morning, the collar of his shirt is noticeably askew as a result. Just moments later, when Martha enters the TARDIS for the first time, the collar is neat again, without him having done anything. (00:41:00)
Continuity mistake: When Martha is talking to the Doctor, who is posing as a patient, about her encounter with him in the street earlier, which he doesn't remember, she takes her stethoscope off her neck. The camera cuts to the Doctor, then back to her, and she's taking it off again. (00:04:15)
Continuity mistake: When the Doctor is looking out the window while asking Martha if there's a balcony on the floor of the hospital they're on, in close-ups of him only his right hand is visible, resting on the sill between two windowpanes, and his left arm is by his side. In a wide shot from outside looking in, his left arm is stretched out with his left hand gripping the divider between two windowpanes, in a spot where it should have been visible in the preceding shot. (00:10:05)
Continuity mistake: When the Doctor and Martha open the doors to the balcony, in a shot facing them, Martha lets go of the handle of her door and it swings completely open. In the next shot, from behind, Martha is still holding the doorknob. (00:10:35)
Continuity mistake: When the Doctor is telling Martha that he was just wandering and not looking for trouble, in the wide shot, he's rubbing his chin. In the close-up immediately afterward, his hand has jumped to his hair. (00:19:45)
Continuity mistake: When Martha and the Doctor are talking in the alley at the end, he's leaning on the TARDIS. His exact position keeps changing between shots. (00:39:10)
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.