Cannot download 1080p iTunes movies from iCloud to iPhone

So when I try to download a movie from iCloud to my iPhone 6s Plus, it only gives me 2 download options: Standard Definition or HD 720p. It won't let me download the 1080p versions. Yes... I have gone on iTunes and MADE SURE I checked the box to prefer 1080p over 720p. Then I signed out of iTunes on my iPhone and signed back in and it still is downloading in 720p. For example, I just downloaded Deadpool. It has three quality options: 1.74 GB (SD); 3.87 GB (720p HD); 4.18 GB (1080p HD). So the movie is 100% available in 1080p. Now... When I go to the purchased section on my iPhone and try to download the movie, it only gives me TWO options: the SD one at 1.74 GB, and an HD one at 3.87 GB. So it is still defaulting to the 720p version, not the 1080p one. This is only an issue for my iPhone 6s Plus. It downloads the 4.18 GB 1080p version on my iPad Pro, heck, even my 5th generation iPod touch gets the 1080p version and it has a sub-720p screen. I'm guessing this is just some bug that is so picky most people won't notice. Everyone out there - is this happening to anyone else? If you have purchased an HD movie and download the HD version from the purchased section, does it download the 720p version or the 1080p version?