Add to vimrc:
(If not fixed, while in vim :echo $TERM to see what to replace with "screen")

" Handle tmux $TERM quirks in vim
if $TERM =~ '^screen'
    map <ESC>OH <Home>
    map! <ESC>OH <Home>
    map <ESC>OF <End>
    map! <ESC>OF <End>
endif