No problem. Running the attached test script on latest master, Windows 10 1803, several errors like this are logged:

Exception in callback _ProactorBaseWritePipeTransport._loop_writing(<_OverlappedF...events.py:479>)
handle: <Handle _ProactorBaseWritePipeTransport._loop_writing(<_OverlappedF...events.py:479>) created at %USERPROFILE%\source\repos\cpython\lib\asyncio\proactor_events.py:373>
source_traceback: Object created at (most recent call last):
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\base_events.py", line 555, in run_until_complete
    self.run_forever()
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\base_events.py", line 523, in run_forever
    self._run_once()
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\base_events.py", line 1750, in _run_once
    handle._run()
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\events.py", line 88, in _run
    self._context.run(self._callback, *self._args)
  File "..\..\..\..\Documents\python\test_proactor_force_close.py", line 8, in server_callback
    writer.write(b'hello')
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\streams.py", line 305, in write
    self._transport.write(data)
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\proactor_events.py", line 334, in write
    self._loop_writing(data=bytes(data))
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\proactor_events.py", line 373, in _loop_writing
    self._write_fut.add_done_callback(self._loop_writing)
Traceback (most recent call last):
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\events.py", line 88, in _run
    self._context.run(self._callback, *self._args)
  File "%USERPROFILE%\source\repos\cpython\lib\asyncio\proactor_events.py", line 346, in _loop_writing
    assert f is self._write_fut
AssertionError