It looks like buildbot slave crashs since:
http://buildbot.python.org/all/builders/AMD64%20Windows8.1%20Non-Debug%203.x/builds/23
or
http://buildbot.python.org/all/builders/AMD64%20Windows8.1%20Non-Debug%203.x/builds/22

Changes: changeset a1b76c1c3be8409565af71b02b84685233276120

======================================================================
FAIL: test_env_var_debug (test.test_asyncio.test_base_events.BaseEventLoopTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "B:\buildarea\3.x.ware-win81-release\build\lib\test\test_asyncio\test_base_events.py", line 680, in test_env_var_debug
    PYTHONASYNCIODEBUG='')
  File "B:\buildarea\3.x.ware-win81-release\build\lib\test\support\script_helper.py", line 135, in assert_python_ok
    return _assert_python(True, *args, **env_vars)
  File "B:\buildarea\3.x.ware-win81-release\build\lib\test\support\script_helper.py", line 121, in _assert_python
    err))
AssertionError: Process return code is 3221225477
command line: ['B:\\buildarea\\3.x.ware-win81-release\\build\\PCbuild\\amd64\\python.exe', '-X', 'faulthandler', '-c', 'import asyncio\nloop = asyncio.get_event_loop()\nprint(loop.get_debug())']

stdout:
---

---

stderr:
---
Fatal Python error: Segmentation fault

Current thread 0x00000390 (most recent call first):
  File "B:\buildarea\3.x.ware-win81-release\build\lib\functools.py", line 423 in decorating_function
  File "B:\buildarea\3.x.ware-win81-release\build\lib\ipaddress.py", line 1963 in IPv6Address
  File "B:\buildarea\3.x.ware-win81-release\build\lib\ipaddress.py", line 1869 in <module>
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 661 in exec_module
  File "<frozen importlib._bootstrap>", line 673 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969 in _find_and_load
  File "B:\buildarea\3.x.ware-win81-release\build\lib\ssl.py", line 90 in <module>
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 661 in exec_module
  File "<frozen importlib._bootstrap>", line 673 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969 in _find_and_load
  File "B:\buildarea\3.x.ware-win81-release\build\lib\asyncio\sslproto.py", line 5 in <module>
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 661 in exec_module
  File "<frozen importlib._bootstrap>", line 673 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969 in _find_and_load
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1016 in _handle_fromlist
  File "B:\buildarea\3.x.ware-win81-release\build\lib\asyncio\proactor_events.py", line 16 in <module>
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 661 in exec_module
  File "<frozen importlib._bootstrap>", line 673 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969 in _find_and_load
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1016 in _handle_fromlist
  File "B:\buildarea\3.x.ware-win81-release\build\lib\asyncio\windows_events.py", line 13 in <module>
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 661 in exec_module
  File "<frozen importlib._bootstrap>", line 673 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969 in _find_and_load
  File "B:\buildarea\3.x.ware-win81-release\build\lib\asyncio\__init__.py", line 46 in <module>
  File "<frozen importlib._bootstrap>", line 222 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 661 in exec_module
  File "<frozen importlib._bootstrap>", line 673 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969 in _find_and_load
  File "<string>", line 1 in <module>
---

Note that it's not necessarily that changeset; I think build 22 is around when the buildbot started actually doing non-debug builds (the buildmaster and buildslave scripts in Tools/buildbot had no support for a non-debug build before then).

I'll try to run the tests a little further back soon.

Presumably it's from the C implementation of lru cache

Actually, it looks like it's due to PEP 492:

C:\Users\Zachary\code\hg.python.org\3.5>hg bisect -b
The first bad revision is:
changeset:   96411:d1959cafc68c
branch:      3.5
parent:      96407:e59966bb6de5
parent:      96410:b7b73029c825
user:        Yury Selivanov <yselivanov@sprymix.com>
date:        Sat May 30 21:02:34 2015 -0400
summary:     Issue 24004: Support Awaitables (pep 492) in @asyncio.coroutine decorator

Not all ancestors of this changeset have been checked.
Use bisect --extend to continue the bisection from
the common ancestor, 943fa0e8b6a4.

Hi Zachary,

This is extremely strange.  The test doesn't even start the loop, it only creates it, and prints out what 'get_debug' says.

It can't be 'sys.set_coroutine_wrapper' either, as it's only called when a loop is running, or when it's about to start/stop running.

The change in "96411:d1959cafc68c" can only affect running coroutines, but I don't think the tests invokes any.

asyncio itself does not even have any 'async def' functions (only in test_pep492.py)...

Well, whatever it was, 44253ce374fc21402c15cbce9c2be0e184610882 seems to have fixed it.  As of build 35 on 3.x and build 31 on 3.5, test_asyncio passes on the Non-Debug Windows bot.