You can reproduce the error wih this env
mac os x 10.11
tmux 2.1
python 2.7
powerline 2.2
Sorry I found it was fixed in v2.3
I still have this in powerline 2.5.
I have this issue too in v2.5 just like @erikw
@nether-cat The solution for me was to completely remove all my powerlin configuration files and copy the new templates. The bug was due to some old issue with these configuration files.
@erikw I even did that. But thanks to your reply I doubled checked what I had done and I realized, that I had not killed the powerline-daemon after doing that. It's working now :)