Continuity: Harry says that Dobby had left the Malfoys to give him warnings two years ago, but that happened in book two, which was three years ago. Dobby was still employed by the Malfoys when he arrived to warn Harry.

Continuity: In chapter 30 of the American hardcover, Harry and Hermione find seats in the topmost row at the Quidditch match. But when Hagrid comes to tell them about Grawp, he squeezes his way through the row behind them. If Harry and Hermione are in the topmost row, there can't be a row behind them.

Continuity: In chapter 9, when Harry lets Hermione borrow Hedwig, Harry remains bent double until he hears Hermione close the door. However, when he hears Hermione and Hedwig had gone, he hurries across the room and closes the door, but the door had already been closed.