We've been informed that the title for Half-Blood Prince, the film, in Spain, has been changed to be more in line with the translated book. Before it was Harry Potter y el Príncipe Mestizo, which translated to Half-Blood Prince, but now the film will be called Harry Potter y el Misterio del Príncipe (the Prince Mystery), which is the title of the Spanish sixth Harry Potter book.

Source: Blog Hogwarts