Documented instance of Internet Explorer 5.22 on a Mac transmitting an HTTP Referer header from a link on a secure page (https): http://www.gadgetopia.com/2003/12/23/OutlookWebAccessPrivacyHole.html This is clearly covered in the HTTP 1.1 spec (RFC 2616), Section 15.1.3, "Encoding Sensitive Information in URI's": "Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol."
