Ruby on Rails: stripping file extension from image request and redirecting to 404

An image is located in the Rails directory at public/images/subDir/X.png.

In the development environment, this loads perfectly.

In production, Rails strips off the file extension (.png) and redirects requests to public/images/subDir/X instead, which results in a 404.

How do you get Rails to not redirect image requests like this?

We're using RoR 3.2.x.