cyclic __proto__ ... disallowed?

gistfile1.js

Foo = { baz: 2 /*, .. */ };

// link Bar to Foo
Bar = Object.create( Foo );
Bar.bam = 3;

// link Foo back to Bar
Foo.__proto__ = Bar;
// or, in ES6: `Object.setPrototypeOf( Foo, Bar )`

// throws error here.
// in chrome: "cyclic __proto__ value"
// in ff: [[SetPrototypeOf]] failed on ({baz:2})

Bar.baz; // 2
Foo.bam; // 3

gistfile2.txt

If you were to make a property or method reference against
`Foo` or `Bar` that didn't exist on either, you'd have a
legitimate "infinite recursion" type of error condition.

But, it seems like `Bar.baz` and `Foo.bam` are safe and
should be allowed, no?

I thought the only why access Foo.bam is by mix-in not through prototype inherit.