Responsive Image (Picturefill.js) is not working on scaled image in redactor editor

I have added two image through redactor editor. In which one is original and other one is scaled to small.
Responsive image feature (picturefill.js) is working with non scaled image. But with scaled image its not working.

for example,
non scaled image is loaded in <picture> tag with different resources,
scaled image is loaded in <img> tag, with only one sources.

Is scaled image not working with responsive image feature ?
here is link of page :

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MrKDilkington replied on at Permalink Reply
Hi srjahir32,

I recreated your example and the picture element was used for both the large and resized image.

Based on the following thread, have you modified the way images are handled in Redactor?

Using a clean install and the default Elemental theme, do you still experience the problem?
srjahir32 replied on at Permalink Reply
Hi MrKDilkington,
I really appreciate for always helping me out.

Actually as you have suggested thread, I don't know where to add this code, as it didn't really specified. Can you suggest me files where i can add that code ?