Vue.js version

1.0.18 (same behavior in 1.0.19)

Reproduction Link

v1.0.17 Here it works
v1.0.18 Issue is here

Steps to reproduce

Change the value in the input field

What is Expected?

Being able to mutate the default value for a prop

What is actually happening?

When defining a props attribute with a type(or validator) and a default function that constructs an instance of the specified type, binding the returned default value to an input field(via v-model) does not work properly, ie the input mutations are ignored.

Possible related to #2549?