It has nothing to do with image size. It's the way devices handle exif data within the image. A resize or even a quick crop fixes the issue but its a PITA. It is a known problem on many forums and sites.
Right, but the issue occurs when the site tries to resize the images. If you resize them yourself, you'll never have an issue.
That's how it's worked for me, anyway. No matter what device I upload from--PC, laptop, or iPhone--if I don't resize it 800 pixels or less, it won't work.
Of course, I understand not everyone has the ability to quickly resize images to a specific size.