Tab autocompletion of accented characters in zsh doesn't work

I am not able to properly display autocompleted filenames that contain accented characters like ã in my shell configuration of zsh and oh-my-zsh.

I've created a filename cão.txt to demonstrate this issue. If you're interested, that means dog in Portuguese.

So, when I try to autocomplete like cat c<tab>, this happens:

% cat ca<0303>o.txt
hi dog

and echo $0 gives me: -zsh

But, if I go to a "plain" zsh session the exact same autocomplete works ok:

% zsh
% echo $0
zsh
%  cat cão.txt
hi dog

My locale is like this:

LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL="en_US.UTF-8"

and the LANG variable I tried it empty, with "en_US.UTF-8" and also "pt_PT.UTF-8". Also, I double-checked the locale settings are exactly the same before and after going to the "plain" zsh session.

Also it works the same way in both the default terminal OSX application and iTerm2.

I'm using zsh version 5.0.7.

Here is my .zshrc file, as well as other dotfiles I'm using.

I've tried uninstalling oh-my-zsh and install it in either the automatic and manual way, always with the same problem of displaying accented characters with autocomplete.