Only the first image path linked in srcset gets rewritten with CDN-URL

[ulilu]

Hi there,
I just installed the CDN plugin to work with KeyCDN (via pullzone). Everything is fine, except for images that have srcset-attributes. When I add "srcset" as tag attribute in the plugin settings, only the first image path inside srcset gets updated with the CDN path - all other paths remain the same (= relative paths on the root server).

[ulilu]

Addendum

This is the twig command that produces the srcset:

{{ page.media[page.header.image].quality(60).derivatives(400, 1600, 300).sizes('100vw').html(page.title, page.title, page.header.imagealign) }}