Prefix key `C-S-c` is echoed as `C-c`

When I press C-S-c, the echo area shows only C-c. Things like C-S- selection do work, however.

I'm in Ubuntu 14.10 Utopic Unicorn in case this helps.

Here's the code for the key binding (for multiple cursors) in my .emacs:

;; multiple cursors
(require 'multiple-cursors)
(global-set-key (kbd "C-S-c C-S-c") 'mc/edit-lines)

Copyright Notice：Content Author:「paula.em.lafon」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/33925763/prefix-key-c-s-c-is-echoed-as-c-c