Enable image caching in development mode in Rails 3.1
The only way I've seen to manipulate the Cache-Control header for assets is by configuring static assets with:
config.serve_static_assets = trueconfig.static_cache_control = "public, max-age=3600"
http://code.google.com/p/chromium/issues/detail?id=102706
This seems to be a documented issue with chrome. I'm suffering from the same problem: Adding or removing a CSS class that references an image will flash or resize while the image request (which will always return a 304 not modified) is underway.
Sprockets is either going to send caching headers or force revalidation (see the source).
I can see no publicly available options to change this behavior.
To modify this I think you will have to monkey patch Sprockets.
Possibly of greater interest is why Chrome is behaving in that way?