tmux 2.1 mouse mode doesn't work on iterm2

So, this doesn't seem to happen on Terminal.app. I'm using the "new" mouse mode configuration, i.e. setw -g mouse on and bind -n WheelUpPane copy-mode in tmux.conf. This works fine with the wheel on Terminal.app but seems to be broken on iTerm2.

Prior tmux works fine. Let me know if you need further info.