aerosol/vim-powerline — comment on commit b3b896834a5c981420cf98c0114e799da6de2b30
File:  line 0
By Lokaltog:

Powerline files are only sourced once, then cached (and only raw data is cached, not functions or anything else). I'll create a method of providing functions in statuslines, in the meantime you could copy this function to your vimrc. :)