Integration with Responsive images and styles module

I'm using Flexslider 7.x-2 to display multiple images within a single node through the flexslider field formater.
I tried to make the slider adaptive using resp_img module (Responsive images and styles module)

It seems the flexslider formater doesn't integrate properly with resp_img as the responsive flexslider images are computed as :

image.jpg%3Fitok%3DUHo9V-Oe?itok=6pS5XN46

%3Fitok%3DUHo9V-Oe = urlencode (?itok=UHo9V-Oe) : the scheme "?itok=xxxx" appear to be repeated 2 times across the formating process and the images cannot be generated :

Unable to generate the derived image located at
public://styles/photo_serie_custom_user_tablette_1x/public/field/image/polaeva-8305.jpg?itok=UHo9V-Oe.

Is there anything wrong with my configuration ? Or is there any patch available for flexslider or resp_img ?
I'm aware of https://drupal.org/node/1545198 : I don't know if this is dealing with the same problem but anyway it doesn't apply in my case as this is a Flexslider 7.x-1 patch

Thanks for any help.