When Sabrina and Paul and eating at the outdoor cafe, it's raining in the background of all of his close-ups (the road is wet and people have umbrellas open), while it's dry in all of her close-ups.
When Sabrina rides the scooter, the cars in the background keep changing from the wide shots to the long shots and back again all the time.
At 48 minutes, Sabrina, Gwen, Paul, and Travis are all sharing a meal at another outdoor cafe. While they're at the table, it appears to be dry weather. When Gwen walks off and yells to Sabrina, there's a person in the background with an opened umbrella, indicating rain, but it still seems relatively dry. After Gwen kisses the black pigeon and Sabrina is standing next to her, the pavement is very clearly wet and there are a lot of people in the background with opened umbrellas.
During the shopping montage (at 34 minutes), one shot of Sabrina and Gwen running through the crowd has been noticeably flipped. Not only is the yellow and blue striped shopping bag now in her left hand, but an extra near the camera has a shirt with reversed text ("Play 98") on it.
When Sabrina and Paul kiss after he meets his family, Melissa Joan Hart's mic pack is visible in the back of her dress.