Carpe Noctem - S3-E4
Continuity mistake: When the gang rescues Angel and returns him to his normal form towards the end of the episode, Cordelia shocks him unconscious with a taser and he falls to the floor, lying on his front. But when Fred whacks him on the head with her baseball bat, he is suddenly lying on his back.
Plot hole: When Angel is being pursued by the Lilliad demons, he is holding his son Connor and is talking to him in the car. Later on it is revealed that he is in fact holding a teddy bear with a bomb attached to it. If it wasn't his son, why was he talking to it? It couldn't be to fool the Lilliad demons because they wouldn't be able to hear him, as they were in separate vehicles.
Revealing mistake: When Cordelia goes to see Lilah, the eyelashes of her real eye can be seen blinking Underneath her "black" eye after she sits down.
Continuity mistake: When the demon Angel and Groo are chasing crashes through a wall, the resulting hole lets in enough sunlight to force Angel into the shadows. A few shots later, Wesley notices Angel standing in the entrance to the hole. Only a few moments have passed, so Angel shouldn't be able to stand where he is. (00:15:20 - 00:16:20)
Answer: Due to his epiphany, Angel basically had the 'true darkness' he worked so hard to reattain ripped away from him, like his soul was after sleeping with Buffy.