Value of Content-Disposition header:

Content-Disposition: attachment; filename="foo-ä.html"

Test Description:

'attachment', specifying a filename of foo-ä.html, which happens to be foo-.html using UTF-8 encoding.

UA should offer to download the resource as "foo-ä.html". Displaying "foo-.html" instead indicates that the UA tried to be smart by detecting something that happens to look like UTF-8.