Images are not deleted

Image are never deleted using ckeditor with one click upload with the option "Delete unused files".

How to reproduce:
1) upload an image using one click upload
2) save the content
3) edit the content
4) delete the image
5) save the content
6) run cron

Result: the image is still in the file system in sites/default/files/inline/images
Expected: the image should be deleted