iphone4 error on JPG web images while viewport is set with magnification 1 ???

[vkp]

Hi.

I was inform that pages that contain simple JPG images, are shown completely wrong (very low quality) via iphone4. I don't have iphone4, but friends that have it, send me a photo with the problem:
http://xvp.gr/iphone4/iphone4_scrabled_image.jpg

In order to verify the problem we did different experiments. All those are simple HTML pages with or without <meta> "viewport" and parameters, and with different kinds of JPG images (optimized, non-optimized, progressive, sRGB converted etc), even .gif or .png images. In all cases we use <meta> "viewport" and JPG image, we get the image destroyed (very low quality) in iphone4, while in the classic iphone (add different phones as well) all are shown correct. You can review the source code of each experiment, to verify the results:

http://xvp.gr/iphone4/t01.html
http://xvp.gr/iphone4/t02.html
http://xvp.gr/iphone4/t03.html
http://xvp.gr/iphone4/t04.html
http://xvp.gr/iphone4/t05.html
http://xvp.gr/iphone4/t06.html
http://xvp.gr/iphone4/t07.html
http://xvp.gr/iphone4/t08.html
http://xvp.gr/iphone4/t09.html
http://xvp.gr/iphone4/t10.html
http://xvp.gr/iphone4/t11.html
http://xvp.gr/iphone4/t12.html
http://xvp.gr/iphone4/t13.html
http://xvp.gr/iphone4/t14.html
http://xvp.gr/iphone4/t15.html
http://xvp.gr/iphone4/t16.html
http://xvp.gr/iphone4/t17.html
http://xvp.gr/iphone4/t18.html
http://xvp.gr/iphone4/t19.html
http://xvp.gr/iphone4/t20.html
http://xvp.gr/iphone4/t21.html

Thus, the question is:

Does iPhone4 has some kind of bug in displaying correctly JPG images when <meta> "viewport" is set and magnification is set to 1?

Or we miss something that we should know about?...

Can anyone give me an example where the JPG image should be shown correctly, in a viewport of width 320, while the user to be able to move around it in magnification=1?

Thank you for your time.