UPDATE: The Wall Street Journal has confirmed (free subscription required) that this is legitimate, although they say not all IMAX theaters will have to wait until the 29th.
EDIT: As of now, this is NOT confirmed, but we'll keep you posted on official word.
While Harry Potter and the Half-Blood Prince will be out in theaters July 15, fans will have to wait until July 29 to see the movie in IMAX , according to a report from TV Watch Online. Jeff from TV Watch Online emailed IMAX and got this response:
Basically what happened is IMAX Corporation signed a contract with Paramount guaranteeing them a 4 week exclusive window if they filmed parts of Transformers 2 with IMAX cameras onto IMAX film (something that is quite a bit more expensive). Unfortunately that was back when Harry Potter was due to open November 2007 and when Warner Bros. pushed back the opening date Paramount was not willing to renegotiate the contract it had signed with IMAX.