srcset bug in Chrome & FF

[jimmleon]

i have data-srcset with 3 images:
image-480.jpg 480w, image-720.jpg 720w, image-960.jpg 960w
and specified sizes as such: (max-width: 600px) 100vw, (min-width: 601px) and (max-width: 992px) 50vw, 33.3vw
and data-src="image-480.jpeg".

Well, Chrome will never display the 480px image.
On the other hand, i see that Firefox makes a double request: the 480px image as well as the 960px!

Any idea of why is this happening or how to solve this issue?

This plugin is really great in general, however it's a pity if it cannot actually handle such a useful attribute as the srcset. Any help would be really appreciated