This is probably not the case, but is it possible that Quora is intentionally stripping the referer header? Duck Duck Go does just this in the interest of user privacy: why should site X know where I came from and what I was searching? https://duckduckgo.com/privacy.html Seems unlikely in this case but possible.

Incidentally, it seems that encrypted.google.com does this but not regular google. EDIT: This happens for all https->http requests, it's not a google feature (TIL).