Generics return type check with arrow functions

[zerkms]

TypeScript Version: playground (2.1.4-insiders.20161201)

Code

let f1: <T>(a: T) => T = a => 42;

function f2<T>(a: T): T {
    return 42;
};

Expected behavior:

Since those functions are identical I expect both to behave the same: to fail the type check.

Actual behavior:

The f1 type checks fine.

[mhegazy]

Duplicate of #5616