tmux can not display vertical line when split vertical panel

Question

Environment:

• Terminal Client
  • pietty 0.4.0(beta 14) (which is forked from putty)
  • putty 0.63
• OS & tmux version
  • CentOS 6.5, tmux-1.6-3.el6.x86_64
  • ArchLinux, tmux 1.9_a-1

Strange behavior:

• Split a vertical panel.
• It won't display a vertical line between left and right panels.
• When I click on right panels.
• It display a vertical line.

Is there any method to let it always display vertical line?

My tmux.conf

set -g utf8
setw -g utf8 on
set-option -g mode-mouse on
set-option -g mouse-resize-pane on
set-option -g mouse-select-pane on
set-option -g mouse-select-window on
# I've tried the following three settings, all failed.
set -g default-terminal "screen-256color"
#set -g terminal-overrides 'xterm*:smcup@:rmcup@'
#set -g default-terminal "linux"

And the TERM and locale variables inside tmux

$ echo $TERM
screen-256color
$ locale
LANG=en_US.utf8
LC_CTYPE=zh_TW.utf8

Answer 1

In putty/pietty, Turn off the option change settings/Window/Translation/Treat CJK ambiguous characters as wide

Answer 2

From the tmux man page:

The TERM environment variable must be set to ''screen'' for all programs run-ning inside tmux. New windows will automatically have ''TERM=screen'' added to their environment, but care must be taken not to reset this in shell start-up files.

Maybe try changing this and see if it helps?

I've seen other users usually set this in their .tmux.conf so they also get color support:

set -g default-terminal 'screen-256color'