Before Holly Marie Combs decides to get hot and heavy she pulls his shorts down to his ankles. The next scene we see her ripping a condom open with her teeth and he is again wearing shorts while laying back on a table.
During a sex scene involving Sharon, she can be seen putting a condom on what is clearly a prop of some sort (piece of wood, possibly). This error is only visible in some prints of the film including the full-screen VHS version. Other prints crop this out.