Spread operator inconsistency with optional object properties

[Dbuggerx]

In the following code, I'd expect both functions to throw an error, but the spread version works.
Try it

/* @flow */

function failsAsExpected(x: A): B {
  return {
     a: x.a,
     b: x.b,
     c: x.c
  };
}

function shouldAlsoFailButWorks(x: A): B {
  return {
   	...x
  };
}

type A = {
    +a: boolean,
    +b: number,
    +c?: string
}

type B = {
    a: boolean,
    b: number,
    c: string
}

[villesau]

@Dbuggerx this pull request fixes this issue as well: #7298

[nmote]

This now has the expected behavior on master