I had a few problems with KiTTY a clone a PuTTY, and tmux, a terminal multiplexer: pane separators where displayed as ‘q’ or ‘x’ instead of lines. It turns out it’s a PuTTY problem, according to tmux FAQ:

PuTTY is using a character set translation that doesn’t support ACS line drawing.

I had this problem for a while, and I didn’t manage to solve the problem with my old bitmap font: Terminus. Maybe because the font is missing the glythes to draw lines. There were actually a few problems:

1. My old font didn’t have line-drawing glyth (?)
2. PuTTY character translation problem
3. Encoding wasn’t properly detected by tmux

I recently switched to a new font: Source Code Pro by Adobe, which allowed me to fix the problem with the missing glyth. I also had to tweak tmux & KiTTY a little bit. In KiTTY’s settings, in the Windows > Translation Category: set the remote character set to ‘UTF8’, and select the unicode line drawing code points. Make sure your font support line-drawing code point. Start tmux with the -u option to tell it to use UTF-8, and you should be good to go.