imgcat doesn't work in a tmux session

• iTerm2 version: Build 2.9.20151001
• OSX 10.11.0 (El Capitan)
• debug log
• com.googlecode.iterm2.plist file
• tmux 2.0 (from Homebrew)

I try to use imgcat in a tmux session but the image doesn't get correctly displayed. There is like only one line displayed, and for gifs there isn't any display at all. I made a gif to illustrate the situation here