Finger Print Digest not appending with image path in Rails 3.2.22.5

I have a css class declared in a CSS partial named '_city-images.css.scc' :

.city-art {
  background: url(image-path('cities-images.png')) no-repeat;
}

The problem is after compilation of assets via assets:precompile. The path generated by the 'image-path' helper is not generated with finger print.

The path generated is : https://abc.mysite.com/assets/cities-images.png But it should be something like : http://ift.tt/2z9og9l

Before you ask, the issue is only in .css.scss files. All the paths in other files are generating with fingerprints. Finger Printing is enabled as well in production.rb : config.assets.digest = true

I have searched a lot, but couldn't find a solution which worked.

Can any one help?