Vue.js version

1.0.26

Reproduction Link

http://jsbin.com/cavadiwosi/1/edit?html,js,console,output

Steps to reproduce

$vm.$delete('object.key')

What is Expected?

$vm.object.key should not exist
$vm.$set('object.key', value) seems to work fine

What is actually happening?

$vm.object.key doesn't change