Inconsistent Treatment of Shorthand Functions #11062

// A *self-contained* demonstration of the problem follows...
function testFunction(x: string | Function): any {
    if (typeof x === 'string') {
        return {
            key: function (a: any, b: any) {
                // Fine, x is string
                return a[x];
            }
        };
        return {
            key(a: any, b: any) {
                // Fails, x is string | Function here
                return a[x];
            }
        };
    }
}