Wallpapers are not shown if the extension does not match the mime-type

Wallpapers are not shown if the extension does not match the mime-type.

For example, if I set as a wallpaper ~/somepicture.png, and the file is actually a jpeg file, the wallpaper is not shown.
The same happens if it's simply ~/mywallpaper (with no extension).

In particular, I share my compiz settings across various PCs, and symlink ~/wallpaper1.png, ~/wallpaper2.png, ~/wallpaper3.png, ~/wallpaper4.png to the wallpapers I want on each PC. If one of these symlinks points to a jpeg file, it is not shown.

It would be nice if compiz could detect the mime-type of the images itself instead of relying on the actual file extension.