Compilation of function indirection leads to runtime error

[westy92]

TypeScript Version: 2.1.0-dev.20160810

Code
Tried with --target es5 and --target es6

'use strict';

class O {
  constructor(private n: string) { }
  public getA = () => this.n;
  public getZ() { return this.n; }
}

let o = new O('5');

let getB = () => '5';
let getC = () => o.getZ();
let getD = function() { return o.getZ() };

console.log(o.getA());
console.log(getB());
console.log(getC());
console.log(getD());
console.log(o.getZ());
console.log();

function indirect(f: () => string) {
  return f();
}

console.log(indirect(o.getA));
console.log(indirect(getB));
console.log(indirect(getC));
console.log(indirect(getD));
console.log(indirect(o.getZ.bind(o)));
console.log(indirect(o.getZ));

Expected behavior:
A warning or error on transpilation because this will be undefined.
OR
A warning or error on transpilation because we're passing a class instance method as a function parameter.
Actual behavior:
Transpiles and then on run:

5
5
5
5
5

5
5
5
5
5
/home/seth/Desktop/test.js:8
    O.prototype.getZ = function () { return this.n; };
                                                ^

TypeError: Cannot read property 'n' of undefined
    at O.getZ (/home/seth/Desktop/test.js:8:49)
    at indirect (/home/seth/Desktop/test.js:21:12)
    at Object.<anonymous> (/home/seth/Desktop/test.js:28:13)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Function.Module.runMain (module.js:447:10)
    at startup (node.js:148:18)
    at node.js:405:3

[gcnew]

If you add this annotations, it will be an error:

class O {
    constructor(private n: string) { }
    public getZ(this: O) { return this.n; }
}

function indirect(f: (this: void) => string) {
  return f();
}

let o = new O('5');
console.log(indirect(o.getZ)); // Argument of type (this: O) => string is not assignable ...

Sadly automatic inferring of this didn't make it, because of negative performance implications :(. For further information see #6739