Here is the request and response headers

http://www.example.com/get/pdf

GET /~get/pdf HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Referer: http://www.example.com
Cookie: etc 

HTTP/1.1 200 OK
Date: Thu, 29 Apr 2010 02:20:43 GMT
Server: Apache/2.2.14 (Unix) mod_ssl/2.2.14 OpenSSL/0.9.8i DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
X-Powered-By: Me
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Pragma: no-cache
Cache-Control: private
Content-Disposition: attachment; filename="File #1.pdf"
Content-Length: 18776
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=utf-8
----------------------------------------------------------

Basically, the response headers are sent by DOMPDF's stream() method.

In Firefox, the file is prompted as File #1.pdf. However, in Safari, the file is saved as File #1.pdf.html.

Does anyone know why Safari is appending the html extension to the filename?