Our site is multilingual. FR/EN
After installation, we see that there is a 301 redirect from /sites to /fr/sites on the images using the adaptive image effect.

Our slider calls this image
www.domain.com/sites/default/files/styles/slideshow_home_image/adaptive-...

It gets redirected 301 to
www.domain.com/fr/sites/default/files/styles/slideshow_home_image/adapti...

The problem is : Because there is a 301, the image is not cached by the browser. We can't get the 304 - unmodified.
We're not getting this behaviour for images that do not have the adaptive image effect.

Any clue? Thanks!