iterm + tmux isn't allowing me to scroll up with the mouse I recently rebuilt my system and everything works except I can't scroll my (iterm2) terminal window back to look at commands and output that have scrolled off the screen.

Without tmux I can scroll but with tmux I can't

When using vim this isn't an issue as I can scroll back within vim.

For basic terminal (which I don't normally use) the behavior is a little different in that the current line scrolls back to show previous commands, but just that line, not the whole window.

My terminal settings include: 

I do use tmux and I have a detailed .tmux.conf  However I have removed these settings, applied with tmux source-file ~/.tmux.conf,. seen the changes applied (back to default tmux setting) and still have the issue 

My settings include 

set -g mouse on
The recent release of tmux 2.1 changed some of the configuration options. This bit of code (taken from here) restores the previous functionality:

bind -n WheelUpPane if-shell -F -t = "#{mouse_any_flag}" "send-keys -M" "if -Ft= '#{pane_in_mode}' 'send-keys -M' 'select-pane -t=; copy-mode -e; send-keys -M'"  
bind -n WheelDownPane select-pane -t= \; send-keys -M 


Add/place these in the ~/.tmux.conf file

Apply with tmux source-file ~/.tmux.conf