In the final episode of series 7, called 'Something Wicca this way goes' there is a scene in the manor basement where Piper Prue and Phoebe are planning to destroy the nexus when it has entered Zankou. Watch when Zankou throws them across the room, when they land Phoebe is clearly wearing gold high heel wedge style shoes. The shot then cuts back to Zankou and then back the Piper, Phoebe and Paige. If you look now as they are getting up Phoebe is wearing sneakers!!