Audio problem: The lips of the Newscaster's who reports on Conner taking over the sports store do not match what she is saying at all.
Disharmony - S2-E17
Continuity mistake: When Harmony enters Cordelias bedroom, the strap on Corelia's shirt falls off her shoulder and then magically is back in place after the angle change. (00:13:50)
Character mistake: When Faith arrives in LA she is carrying a bag. She puts it on the ground and then steals a man's jacket and wallet. Afterwards however, she leaves without picking up her bag.
Continuity mistake: In the scene where Detective Lockely arrests Angel in the apartment, the window behind them shows that it's daytime. But when Angel jumps out the window, it's night time.
Visible crew/equipment: When Angel gets on the horse to joust, you can see a part of a camera at the right side of the screen. (Widescreen Edition)
Continuity mistake: When Faith is sitting at the window and looks at the piece of broken glass she used to torture Wesley, it has a different shape than the one she first takes to torture Wesley. When she drops it out the window it has its original shape again. (00:33:10)
Revealing mistake: In the scene where Angel fights the demon for the first of his trials, upon cutting the demon in half for the second time he chains the two halves to the walls. When he drags the upper half of the demon to the wall, the green legs of the actor are momentarily visible, when they should have been removed by CGI. (00:29:00)
Sleep Tight - S3-E16
Revealing mistake: When Angel is seen gulping the blood from the cup (right before Lorne tells Angel that Connor needs some papa-love) you can see this is a special-effects cup (it's like one of those freezer mugs, where there's a layer of liquid on the outside). If Angel were really drinking out of the cup the way it's shown, he would have blood all over his lips and it would be running down his chin.
The Cautionary Tale Of Numero Cinco - S5-E6
Factual error: When the mysterious person hands Cinco the business card during the 50's flashback (in the restaurant where he is sitting waiting for business), it says "Wolfram & Hart, Attorney's at Law." Clearly, there should be no apostrophe in "Attorneys" in this context - not a mistake a professional law firm would make.
Disharmony - S2-E17
Continuity mistake: When Cordelia and Harmony are on the couch talking and drinking, the towel on Cordelia's head goes from on her shoulder to behind in the change from wide to close up. (00:10:30)
Continuity mistake: When Cordy throws the knife at the door after Willow leaves, the knife hits at an impossible angle from where it was supposed to have been thrown.
Continuity mistake: When Cordelia looks at the monitor, the reflection of Angelus's cage shows Angelus standing at the bars next to Connor. It cuts to a direct shot, and Angelus is sitting on the ground on the other side of the cage. (00:21:40)
Ground State - S4-E2
Revealing mistake: In 'Ground State' when Gwen is walking towards the lift in Irwin's building you can see Angel's reflection on the shiny door. Vampires don't have reflections, as is demonstrated at various other times in this show.
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)
A New World - S3-E20
Revealing mistake: When Connor runs out of the hotel and Groo and Gunn drag Angel out of the sunlight, Angel's reflection can be seen in the door behind him just as Cordelia steps outside. Angel is a vampire: he should not cast any reflection.
Revealing mistake: When Groo rushes in to battle the tree demon, a cobweb gets stuck to the camera as it pans in.
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.