unable to get agent forwarding on vagrant working - ssh

Question

Despite my best efforts, I cannot seem to get agent forwarding on Vagrant. I'm running OS X with the following vagrant/virtualbox combo:
[chrisshorrock:~]$ vboxwebsrv --version
Oracle VM VirtualBox web service Version 4.2.18
(C) 2007-2013 Oracle Corporation
All rights reserved.
4.2.18r88780
[chrisshorrock:~]$ vagrant --version
Vagrant 1.3.5
Firstly - in my vagrant file I have
config.ssh.forward_agent = true
I've confirmed that my key (on my os x box) is added to my ssh agent with:
ssh-add -L
My ~/.ssh/config file contains the following:
Host 127.0.0.1
ForwardAgent yes
I can connect to outside servers, and have confirmed that something like:
ssh -T git#github.com
Works properly (both locally and remotely indicating that ssh agent forwarding functionality seems correct on the OS X box), however, when I connect to my vagrant instance, I have no such luck:
[chrisshorrock:~]$ ssh -v vagrant#127.0.0.1 -p 2222
OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
debug1: Reading configuration data /Users/chrisshorrock/.ssh/config
debug1: /Users/chrisshorrock/.ssh/config line 35: Applying options for 127.0.0.1
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug1: Connecting to 127.0.0.1 [127.0.0.1] port 2222.
debug1: Connection established.
debug1: identity file /Users/chrisshorrock/.ssh/id_rsa type 1
debug1: identity file /Users/chrisshorrock/.ssh/id_rsa-cert type -1
debug1: identity file /Users/chrisshorrock/.ssh/id_dsa type -1
debug1: identity file /Users/chrisshorrock/.ssh/id_dsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1.1
debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1.1 pat OpenSSH_5*
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA 50:db:75:ba:11:2f:43:c9:ab:14:40:6d:7f:a1:ee:e3
debug1: Host '[127.0.0.1]:2222' is known and matches the RSA host key.
debug1: Found key in /Users/chrisshorrock/.ssh/known_hosts:29
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/chrisshorrock/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug1: Authentication succeeded (publickey).
Authenticated to 127.0.0.1 ([127.0.0.1]:2222).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions#openssh.com
debug1: Entering interactive session.
debug1: Requesting authentication agent forwarding.
debug1: Sending environment.
debug1: Sending env LANG = en_CA.UTF-8
debug1: Sending env LC_CTYPE = en_CA.UTF-8
Welcome to Ubuntu 12.04.3 LTS (GNU/Linux 3.2.0-56-generic x86_64)
* Documentation: https://help.ubuntu.com/
Welcome to your Vagrant-built virtual machine.
Last login: Fri Nov 22 09:58:24 2013 from 10.0.2.2
[vagrant:~]$ ssh -T git#github.com
Warning: Permanently added the RSA host key for IP address '192.30.252.130' to the list of known hosts.
Permission denied (publickey).
I'm at a loss of things to try.

Answer 1

Problem solved. The box was using oh-my-zsh, which had the plugins defined as:
plugins=(git cp command-not-found git-extras gnu-utils history pip python ruby screen ssh-agent svn)
The culprit here was the ssh-agent helper for oh-my-zsh.