When Piper used Leo's power for the 1st time and healed him, he says let's go and orbs out of the attic, but it would have had to have been Piper who orbed since they hadn't swapped back powers yet, and she would not have known how. Additionally, when this really took place, no one orbed, they walked/leaned down the stairs.
The demon couldn't possibly have stepped on the wedding cake topper. When the cake falls in the original scene in Just Harried, you clearly see the topper land under mounds of cake and frosting.
During the visit with the marriage counselor, Piper freezes the room. Leo yells, "what are you doing? We're on the clock!". Seeing as Piper freezes time, this would not be an issue.
When Paige and Phoebe travel back to the day Piper and Leo met she is shocked to see that Phoebe has blonde hair and even makes a remark about it. However, when Paige first met her sisters Phoebe still had blonde hair.
When Piper walks into the Shrink's office, the audience sees her giggling and then apologizes for her laughter. This is quite possibly an error with Holly Marie Combs, and her not being in character. Piper seems off-put and would not be giggling for no reason, especially walking into a shrink's office.