Walt Disney Studio Home Entertainment announced that the release of "Gake no Ue no Ponyo" DVD Special edition was postponed until December on account of the production status. The special edition includes a 12 hour long making movie of Ponyo and a video of Hisaishi Joe's concert. The normal edition will be released on July 3rd as scheduled. The Blu-ray of Ponyo will be released in December as well.

Source: AV Watch

Suzuki Toshio explained in Ghibli official website that the release of the DVD was postponed because they forgot to have permissions of the copyright holders of the music played in the making video. Miyazaki Hayao played numbers of BGM while working on Ponyo. Suzuki learned 10 days before the release date that they hadn't obtained the permissions to use any of those songs. It will take months to acquire them for some non-Japanese songs, so they decided to postpone the release until December.

Suzuki Toshio apologized for making such an elementary mistake.

Source: Ghibli.jp