Wrong session scoped fixtures parametrization

Consider following testing code:

import pytest


@pytest.fixture(scope="session")
def session_wrapper(param1, param2):
    return param1, param2


class TestClass:
    @pytest.fixture(scope="session",
                    params=["p1 inside A", "p1 inside B"])
    def param1(self, request):
        return request.param

    @pytest.fixture(scope="session")
    def param2(self):
        return "p2 inside"

    def test_inside(self, session_wrapper, param1, param2):
        assert session_wrapper == (param1, param2)


@pytest.fixture(scope="session",
                params=["p1 outside A", "p1 outside B"])
def param1(request):
    return request.param


@pytest.fixture(scope="session")
def param2():
    return "p2 outside"


def test_outside(session_wrapper, param1, param2):
    assert session_wrapper == (param1, param2)

Session-scoped fixture session_wrapper is parametrized by param1 and param2 fixtures, which the fixture returns as tuple. Tests check if session_wrapper really returns current param1 and param2 instances. Which is not the case - first session_wrapper instance in new context returns wrong params (from previous context):

$ py.test -vv test_f.py
============================= test session starts =============================
platform win32 -- Python 3.4.3, pytest-3.2.3, py-1.4.34, pluggy-0.4.0 -- c:\program files (x86)\python34\python.exe
cachedir: .cache
rootdir: D:\workspace\businessFactory\calistos, inifile: setup.cfg
plugins: cov-2.5.1
collecting ... collected 4 items

test_f.py::TestClass::test_inside[p1 inside A] PASSED
test_f.py::test_outside[p1 outside A] FAILED
test_f.py::TestClass::test_inside[p1 inside B] PASSED
test_f.py::test_outside[p1 outside B] PASSED

================================== FAILURES ===================================
_________________________ test_outside[p1 outside A] __________________________
test_f.py:37: in test_outside
    assert session_wrapper == (param1, param2)
E   AssertionError: assert ('p1 inside', 'p2 inside') == ('p1 outside A', 'p2 outside')
E     At index 0 diff: 'p1 inside' != 'p1 outside A'
E     Full diff:
E     - ('p1 inside', 'p2 inside')
E     ?      ^^           ^^
E     + ('p1 outside A', 'p2 outside')
E     ?      ^^^    ++       ^^^
===================== 1 failed, 3 passed in 0.13 seconds ======================
Coverage.py warning: No data was collected. (no-data-collected)

If TestClass is at the end of the script (first outside test and context, then inside), equivalent result is achieved:

test_f.py::test_outside[p1 outside A] PASSED
test_f.py::TestClass::test_inside[p1 inside A] FAILED
test_f.py::test_outside[p1 outside B] PASSED
test_f.py::TestClass::test_inside[p1 inside B] PASSED

When session_wrapper has class or function scope, everything works as expected.

Start by reproducing the failure with the provided test_f.py example and compare the two test-ordering cases. Then trace pytest's session-scoped fixture parametrization and context handling; done means both inside and outside tests receive their current param1 and param2 values regardless of collection order.