No compile error thrown when `this` referenced before call to `super` completes

TypeScript Version:

1.8.9

Code
JSFiddle: https://jsfiddle.net/kitsonk/fs9t96ep/
TS Playground: http://goo.gl/X7cgvV

class A {
    constructor(fn: () => void) {
        fn.call(this);
    }
    foo: string = 'foo';
}

class B extends A {
    constructor() {
        super(() => {
            console.log(this);
        });
    }
    bar: string = 'bar';
}

const b = new B();

Expected behavior:
Typescript should guard against the use of this as the call to super has not completed. Thus it should not compile.

Actual behavior:
Typescript compiles this successfully. It works fine when the target is set to es5 but breaks the browser when target is set to es6.
Error is: VM89:55 Uncaught ReferenceError: this is not defined

Start with the TypeScript 1.8.9 reproduction in the issue, using the linked TS Playground or JSFiddle, and compare compilation with ES5 and ES6 targets. Trace how the compiler handles this inside the callback passed to super; done means the invalid ES6 case is rejected while valid constructor usage remains supported.