Problems uploading (additional) cover art

I've tried uploading several alternative cover images to some comic-books. The pictures show up in my own "images" gallery but not in the comics' pages.
 
After uploading those cover images I can press two differing buttons to finish the upload - "my edit queue" and "refresh page".
Pressing either button will bring up the "confirmation" popup, telling me that proceeding will undo all my changes. I cannot do anything else but to press one of the buttons, though.
 
Is that normal?
 
I was able to upload additional cover art without the confirmation popup yesterday. Those also showed up on the respective comic pages.
But today all attempts fail.
I'd be glad if anyone could shine some light on the cause of the problem.

It will always tell you your changes have been accepted and to refresh the page. You cannot add credits or info to the issue at the same time as a new cover image. Since you do not have live edit, any cover you submit will go to be moderated by one of us.