According to my understanding of RFC 822, the following is encoded correctly:
Content-Disposition: attachment;filename="foo\" \"bar.html"
The decoded value for the filename attribute should be:
But instead it is decoded as:
Firefox an Opera both get it right.
File names in Content-Disposition are handled not by open source WebKit, but by Apple system frameworks. Could you please file this bug at http://bugreport.apple.com instead?
If not, someone else can do it, but it is better when a bug is linked to its original reporter.