Pasted linefeeds causing the Justify command to be executed is an effect of of Putty inverting the sense of Control on the cursor keys. See http://sourceforge.net/p/tmux/tmux-code/ci/master/tree/FAQ and search for "in putty" (without the quotes).
If you find a way to make nano with Putty behave normally, please report back. Otherwise you may wish to apply the patch posted here: https://lists.gnu.org/archive/html/nano-devel/2015-04/msg00000.html -- http://www.fastmail.com - Send your email first class -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
