The hi def DVD industry never fails to disappoint. Because now even the consumers who are versed in the differences between Blu-ray and HD DVD—those who can tell a blue box from a red one with ease—are also getting shat on by a mixed up industry. Numerous reports have surfaced that a new $100+ Harry Potter box set has a fourth disc in HD DVD format—that's Goblet of Fire for those interested. It looks like even Warner Bros' conservative route of supporting both formats has its risks.

Source- http://gizmodo.com/gadgets/oops/harry-potter-blu+ray-includes-unintended-hd-dvd-334017.php