Bug 357312

See the original image at https://drive.google.com/file/d/0B0Jnpz9ldbuHN29mM3NJdUlWUU0/view?usp=sharing and the flipped version at https://drive.google.com/file/d/0B0Jnpz9ldbuHaUdjMkFsV3dncjQ/view?usp=sharing .

Both are PNG images. The first one is scanned. Then I copied it, opened the copy in Gwenview and rotated it twice, obtaining the second image.

I called `identify -verbose` from Imagemagick on both images. The (abbreviated) diff between the two calls is below:

1c1
< Image: image_original.png
---
> Image: image_flipped.png
6,7c6,7
<   Resolution: 118.11x118.11
<   Print size: 21.59x29.7011
---
>   Resolution: 31.89x31.5
>   Print size: 79.9624x111.365
(...)
80c80
<     png:pHYs: x_res=11811, y_res=11811, units=1
---
>     png:pHYs: x_res=3189, y_res=3150, units=1
(...)

The metadata has changed. This shouldn't have happened.

Reproducible: Always

Steps to Reproduce:
1. Open the attached image in Gwenview
2. Rotate it twice (to flip it upside-down)
3. Save the rotated copy
4. Call `identify -verbose` on both images
5. Observe the difference

Actual Results:  
The metadata has changed.

Expected Results:  
Metadata should have stayed the same.