I had a website i was working on http://www.indiansummerfestival.nl and i used a body background image in the top header image.
In every browser and on any Android device the body background image was scaled proportionally with the zoomlevel of the website on the device/screen.
But on iPhone and iPad the body background image was scaled to 100% width… On an iPhone the site was properly zoomed out to fit the width of the screen, but the body background image zoomed out more.. this messed up the design.
After spending some time figuring out what could cause this i finally found the solution.
When you save your jpeg as a Progressive jpeg it worked as expected.