Hi Norbert,
I'm quite don't get you here, Did you mean as you adjust image to be 100% it won't display in the front end?Can you give us some steps on how to replicate this issue, so we can reproduce it locally?
Or is it possible for you to provide us with the back end and FTP access to your site to check on this issue?
You can add the information needed by edit your first post in the Details section or you can just include your site's access once at
http://stackideas.com/dashboard/site rather than needing to keep adding them in your replies