Continuity mistake: When Courtney comes into The Caretaker's room in search of paper towels, there is a "keep out" sign (reading "Go Away Humans") hanging in the window of the inner door. When the Doctor is talking to her just before she leaves, the sign is missing. Over the course of the rest of the episode, the sign proceeds to appear and disappear a few more times. (00:15:50)
Time Heist - S8-E5
Continuity mistake: Near the end, when the Doctor and Clara are standing by the TARDIS on the planet they took the Teller and its mate to, Clara's hands go from touching the buttons on her jacket to loosely clasped lower down. In the third shot of her, they return to the first position. (00:44:28)
Deep Breath - S8-E1
Continuity mistake: Vastra hands the police inspector a bag of sonic lanterns, to be used to contain the T. Rex. In the next shot, looking at the TARDIS on the riverbank, he's not holding it. (00:02:15)
In the Forest of the Night - S8-E10
Continuity mistake: When Clara mentions worrying about a witch in a gingerbread house while she and the Doctor are searching for Maebh, the phones she is holding switch hands between shots. (00:20:11)
Continuity mistake: During Clara's first conversation with Danny, the folders in her hands are unmarked in close-ups, but have labels on them in wide shots. In addition, the folders and newspaper she's holding keep changing position between shots. (00:07:30 - 00:08:26)
Continuity mistake: When the Doctor shows Clara the "listen" written on one of his blackboards, the handwriting is different to when it was first shown. (00:07:07)
Time Heist - S8-E5
Continuity mistake: After Delphox taps on the glass to awaken the Teller, her fingers close as her hand drops below shoulder level. After the angle change, her hand is above shoulder level, index finger extended. (00:06:03)
Continuity mistake: When Clara exits the TARDIS in Sherwood Forest for the first time, she closes the door. Shortly thereafter, when Robin draws his sword on the Doctor, the door has opened itself. (00:04:24)
Continuity mistake: When Robin Hood has finished introducing the merry men to the Doctor and Clara, Clara says "You really are Robin Hood and his merry men" and she is shown with her arms parted away from each other. In the next shot, her arms are suddenly closer to her. Then in the next shot, her hands are now closed together. (00:08:25)
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.