Since this issue is bordering off-topic now, I'm going to post this question on Emacs.SEthis question on Emacs.SE. The underlying issue though still concerns the API. I believe these two issues have the same cause, but if I should post this as a separate question for tracking purposes, just let me know.
(sx-method-call "answers"
:id 7192
:submethod "upvote"
:auth 'warn
:url-method 'post
:keywords (list (cons 'preview 'true)) ;; NOTE
:site "emacs")
=>
[((question_id . 7189)
(answer_id . 7192)
(creation_date . 1420761994)
(last_edit_date . 1420762419)
(last_activity_date . 1420762419)
(score . 4)
(is_accepted . t)
(owner
(link . "http"https://emacs.stackexchange.com/users/105/drew")
(display_name . "Drew")
(profile_image . "https://www.gravatar.com/avatar/32a8e553d85d193ee5ae1533ce6ec158?s=128&d=identicon&r=PG&f=1")
(user_type . "registered")
(user_id . 105)
(reputation . 6689)))]
(sx-method-call "answers"
:id 7192
:submethod "upvote"
:auth 'warn
:url-method 'post
:keywords (list (cons 'preview 'false)) ;; NOTE
:site "emacs")
=>
[((question_id . 7189)
(answer_id . 7192)
(creation_date . 1420761994)
(last_edit_date . 1420762419)
(last_activity_date . 1420762419)
(score . 3)
(is_accepted . t)
(owner
(link . "http"https://emacs.stackexchange.com/users/105/drew")
(display_name . "Drew")
(profile_image . "https://www.gravatar.com/avatar/32a8e553d85d193ee5ae1533ce6ec158?s=128&d=identicon&r=PG&f=1")
(user_type . "registered")
(user_id . 105)
(reputation . 6689)))]
(sx-method-call "answers"
:id 7192
:site "emacs")
=>
[((question_id . 7189)
(answer_id . 7192)
(creation_date . 1420761994)
(last_edit_date . 1420762419)
(last_activity_date . 1420762419)
(score . 4)
(is_accepted . t)
(owner
(link . "http"https://emacs.stackexchange.com/users/105/drew")
(display_name . "Drew")
(profile_image . "https://www.gravatar.com/avatar/32a8e553d85d193ee5ae1533ce6ec158?s=128&d=identicon&r=PG&f=1")
(user_type . "registered")
(user_id . 105)
(reputation . 6699)))]
Cross-reference vermiculus/sx.el#223
, Emacs.SE questionEmacs.SE question