Image editor shows a broken image icon.

I know the cause of the broken image. I just don’t know how to fix it.

The page /wp-admin/admin-ajax.php?action=imgedit-preview&_ajax_nonce=4bb48625f0&postid=561&rand=59216 sends an image allright, but somehow its header starts with an UTF-8 Byte Order Mark and thus preventing the browser to see it as an image (faulty header/encoding).

The response header gives me this:

Accept-Ranges:none
Cache-Control:no-cache, must-revalidate, max-age=0
Connection:keep-alive
Content-Length:16753
Content-Type:image/jpeg
Date:Thu, 02 Apr 2015 08:02:32 GMT
Expires:Wed, 11 Jan 1984 05:00:00 GMT
Persistent-Auth:true
Pragma:no-cache
Server:Microsoft-IIS/8.5
X-Content-Type-Options:nosniff
X-Frame-Options:SAMEORIGIN
X-Powered-By:ASP.NET
X-Powered-By:PHP/5.6.7
X-Robots-Tag:noindex

This also shows my server setup. Yes, IIS, I know…

If I save the file generated by the abovementioned URL and I open it up in Notepad++, change the encoding to ANSI and save it, the problem is fixed. The JPEG is readable again.

I don’t have not enough knowledge to mess around in the core files myself.

There are no hooks into the image saving or creating. Thumbnails and uploading files works fine in the admin.

What could I try to fix this? I can’t host it on any other system though.

Be gentle, first post. Thanks in advance!