I'm on OS X Mountain Lion, running the included ZSH shell (4.3.11) with Oh-My-ZSH installed over the top.
When using tab completion with commands such as homebrew, when ZSH lists the available commands, it is also duplicating the command. For example:
$ brew {tab}
will result in:
$ brew brew
[list of homebrew commands]
I'm unsure what is causing this error, as when I resize the terminal window, the first instance of the command name disappears.
If I hit backspace when the duplicates are displayed, I can only delete the second instance of the command, zsh won't let me backspace any further. Also, if I do remove the duplicate with backspace, zsh then acts as if there is no command typed at all.
My .zshrc along with all my other .configuration files can be found at https://github.com/daviesjamie/dotfiles
UPDATE: I found this post about someone having the same problem on Ubuntu. However, I don't understand the given solution, and I'm not even sure if it applies to my set up?
The problem is likely to arise from misplaced %{ %} brackets that tell zsh that text inside has zero width. The only things that should be enclosed in them are escape sequences that change color or boldness of the text. If you are using new zsh (>=4.3.{unknown version}) I would even suggest to use %F{color}...%f, %K{color}...%k, %B...%b instead of %{${fg[green]}%} or what you have there.
The problem with them is that there is no way to query the terminal with a question like “Hey, I outputted some text. Where is the cursor now?” and zsh has to compute the length of its prompt by itself. When you type some text and ask zsh to complete zsh will say terminal to move cursor to specific location and type completed cmdline there. With misplaced %{%} brackets this specific location is wrong.