Revelations - S3-E7
Corrected entry: At the end of the episode, we find out that Gwendolyn Post was kicked out of the Watchers' Council for misuse of dark power and that the Council had informed everyone of the fact via memo. If that's the case, then why would she use her real name when she arrived in Sunnydale? Wouldn't she be worried that Giles would recognize her?
Revelations - S3-E7
Corrected entry: In 'Revelations', after Mrs. Post attacks Giles, when Buffy finds him he manages to tell her that living flame must be used to destroy the Glove of Mynhgon before the paramedics take him away. Since Angel already knew this, wouldn't it have been much more useful if he had warned her that Mrs. Post was an imposter?
Correction: This mistake falls under the "why" rule. Giles took a nasty knock to the head and is currently in an emergent medical situation, so it's not surprising that he isn't thinking clearly. In this state, it is more important to tell Buffy how to destroy the Glove immediately and prevent it from falling into anyone's hands than to tell her to keep it away from one specific person.
Correction: Giles says the Council "swears there was a memo." It's quite possible that this was just the Council trying to cover itself, since there was no communication to agents in the field - the event was so obvious to people in the Council that they didn't think it necessary to make a specific communication about it.
Phoenix