Subject: two dashes appear after long y-or-n-p's

From: [email-masked]
Date: Thu, 30 Sep 2010 07:31:40 +0800

(y-or-n-p "this short question is quite normal ")
(y-or-n-p "however, with this longer question, be it containing
newlines or not, if it is beyond a certain width, like this one here
is on my terminal, a very funny \"--\" appears after the question.
Test it with C-x C-e OK? ")
It doesn't happen with yes-or-no-p.
emacs-version "24.0.50.1"