Warner Bros. recently postponed the release of the sixth film in the Harry Potter series, Harry Potter and the Half-Blood Prince, from Nov. 21 to July 17 next summer. Unfortunately, sister company Entertain- ment Weekly didn’t get the word on time and promotes the film in its fall roundup issue. At left, Daniel Radcliff, left, Rupert Grint and Emma Watson in a scene from Harry Potter and the Order of the Phoenix.

AP / Murray Close

Maybe Harry Potter should have brought a note from his parents saying he would be missing school.

Warner Bros. gave Harry the school year off, announcing last week it was bumping the sixth movie in the series from fall to next summer. But Entertainment Weekly — which shares the studio’s parent company, Time Warner Inc. — was unaware, featuring Potter star Daniel Radcliffe on the cover of its Aug. 22-29 fall-preview issue.

The magazine leads off the issue with a six-page spread pegged to Harry Potter and the Half-Blood Prince, which Warner Bros. last week moved from its Nov. 21 release date to July 17, 2009.

The studio had been considering the date change for three or four weeks, “but it really didn’t kind of get on the front burner until sometime within the last seven days,” Dan Fellman, Warner Bros. head of distribution, said Sunday.

Entertainment Weekly’s “deadline must have been earlier than the decision, earlier than when we started to get serious about making the decision,” Fellman said.

An Entertainment Weekly spokeswoman did not immediately return phone and e-mail messages seeking comment.

The magazine’s online edition added a preface about the date change to the Harry Potter story. It also had a laugh or two about the lack of communication between two Time Warner outfits.

“In an irony sure to set blogger hearts beating giddily, the film graces the cover of EW’s new fall preview issue,” reads an entry on the magazine’s Hollywood Insider blog. “EW and Warner Bros. share a parent company, but they clearly do not share, you know, important ... information.”

The blog goes on to joke that the date change will leave Entertainment Weekly “readers in possession of a ‘Dewey Beats Truman’ collectible.” It also notes that British film magazine Empire features Harry Potter on its current cover, though that issue touches on big 2009 releases as well.

Warner executives said the date change was a business decision and not due to any production delays on Half-Blood Prince. A recent Writers Guild of America strike had delayed production on some films, leaving a lighter lineup during 2009’s busy summer season, Fellman said.

The July 17 release — the same weekend Warner Bros. debuted its blockbuster The Dark Knight this summer — offered better box-office potential for Half-Blood Prince, Fellman said.

The change left a hole in Hollywood’s overall schedule for Nov. 21, the week before Thanksgiving, one of the busiest weekends for theaters.

But fantasy fans will not have to do without: A day after Half-Blood Prince moved out, Summit Entertainment’s vampire romance Twilight, based on another best-selling series of books, moved in, switched from its scheduled Dec. 12 release to Nov. 21.