Other mistake: In the episode "The Shroud Of Rahmon," when Angel changes into his vampire face, his teeth don't change into fangs. (00:33:55)
Disharmony - S2-E17
Other mistake: When Harmony spills her pig's blood on the keyboard, the computer shorts out, and the monitor flickers off, but the mouse cursor is still visible. (00:25:35)
Disharmony - S2-E17
Other mistake: At the very end, as Angel walks out the door he reflects in the panes of glass on the door. (00:42:10)
Other mistake: Both times we see Lindsey shaving, once before his hand transplant and once after, his reflection in the bathroom mirror isn't in fact a reflection. He is wearing a bracelet on his left wrist, but in the mirror it is on his right wrist.
Other mistake: Later in the day when Cordy has recovered a little and is cleaning, Angel says something about seeing a reflection in the picture. We hear Cordy say, "What do you want," but the subtitles say, "What do you what?"
Other mistake: The Chinese writing shown tattooed all over Wo-Pang's body is nonsense (a small number of random characters repeatedly jumbled together), although Wesley reads it as if it is language. (Although one might argue that the writing is meant to be some sort of code, there is no evidence in the show itself to suggest that, and Wesley refers to "translating" rather than "decoding" it; for these reasons it is more likely to be simply a mistake rather than an intentional decision.) (00:16:40)
Other mistake: Angel implies that Wesley told him the device will kill Illyria. But this Angel is from earlier in the timeline, as shown when he tries to tell Wes and Spike things they have just told their Angel. So Wes did not tell this Angel that the Mutari generator will kill Illyria. Angel should know nothing about it. (00:36:30)
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.