Web Browser reports PNG image as JPG.

I noticed this whilst looking at this image: http://files.myopera.com/wadaka/albums/833597/asdasd.png

Some text reports this image as being PNG, whilst other text reports it as JPG. Other PNG images do not have this issue.

For example, the file name ends with .png, and yet the tab contains the text "JPEG image" next to it. Also, right-clicking and selecting "view image info" shows the image type as "image/png" on the General tab and "JPEG image" on the Media tab.

Is this a problem with the image itself using the wrong extension? If not, is it an upstream (Firefox) issue?