I have the same question. And I found one more anoying thing, I set in media preferences 2 sizes for the images (Medium and Large), but as i have a responsive theme and want to supply 2x images for retina displays my images are double in size, so my Large image size is 1600px and then with css is set to 50% of this size to look as 800px. I found that if I have a $content_width= 900 the size Large is no longer 1600px, is automatically set to 900, the medium size is not modified and is 1200px (bigger than the content–width). So i removed the $content_width function…
