Deliberate mistake: With John Cusack leaning to the side to pull Diane Lane and the dog from the water, the rowing scull should have nearly tipped over, yet it leans only slightly. Later in the same scene, the normal instability of such boats can be seen when tipping occurs to a greater degree simply from the dog moving.
Audio problem: In the scene where everyone's singing the theme to the Partridge Family, Bobby gets up and walks over to a two-keyboard organ and starts playing on the top row. What we hear is piano. It's possible that the organ was set to emulate piano, but he never turned it on first. It's also pretty clear that he's not actually playing anyway, as his keystrikes aren't matching up with what we hear.