stub.unstub() doesn't revert to the original function

I'm using the stub module (http://ift.tt/1Lkev9l) to monkey patch the requests.get() function on my tests.

On different tests I want requests.get() to return different values, so I use stub.stub() in each test case is required. The problem is: it always returns the same value when running the tests with nosetests (apparently the one of the first run of stub.stub()).

A simplified version of my code would be:

common.py:

import stub
@contextlib.contextmanager
def stubbed(target, replacement):
    stub(target, replacement)
    try:
        yield
    finally:
        target.unstub()

test_1.py:

def test_something_returns_200():
    response = requests.Response()
    response.status_code = 200
    with stubbed(requests.get, lambda _: response):
        assert function_under_test().status_code == 200

test_2.py:

def test_something_returns_500():
    response = requests.Response()
    response.status_code = 500
    with stubbed(requests.get, lambda _: response):
        assert function_under_test().status_code == 500

For some reason it will always return 200.

If I try to modify test_something_returns_500() to call requests.get.unstub() before calling stubbed() it fails with:

AttributeError: 'function' object has no attribute 'unstub'