AWS cloudFormation doesn't work with official Centos 6 AMI

I can't get the most simple cloudFormation UserData block to work with Centos 6 AMI.

"UserData" : {"Fn::Base64" : { "Fn::Join" : ["",[
    "#!/bin/bash -ex","\n",
    "sudo touch /root/aws-test.txt"]]}
}

It works fine with Amazon Linux but nothing happens with the Centos AMI. Any suggestions?