Can't read file as teacher when student edited file after teacher

[olmokramer]

When I create a file as teacher that doesn't exist in the student's submission and then edit the same file as student, then the file becomes unreadable as the teacher.

cgfs traceback:

Traceback (most recent call last):
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/fuse.py", line 495, in _wrapper
    return func(*args, **kwargs) or 0
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/fuse.py", line 511, in getattr
    return self.fgetattr(path, buf, None)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/fuse.py", line 759, in fgetattr
    attrs = self.operations('getattr', self._decode_optional_path(path), fh)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/fuse.py", line 972, in __call__
    ret = getattr(self, op)(path, *args)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgfs.py", line 1356, in getattr
    return self._getattr(path, fh)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgfs.py", line 1382, in _getattr
    attrs = file.getattr(submission, query_path)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgfs.py", line 896, in getattr
    super(File, self).getattr(submission, path)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgfs.py", line 68, in getattr
    stat = cgapi.get_file_meta(submission.id, path)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgapi.py", line 193, in get_file_meta
    self._handle_response_error(r)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgapi.py", line 164, in _handle_response_error
    raise CGAPIException(request)
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/codegra_fs/cgapi.py", line 128, in __init__
    data = response.json()
  File "/home/olmo/code/CodeGra.fs/env/lib/python3.6/site-packages/requests/models.py", line 892, in json
    return complexjson.loads(self.text, **kwargs)
  File "/usr/lib64/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib64/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib64/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

server traceback

127.0.0.1 - - [19/Feb/2018 17:54:17] "GET /api/v1/submissions/2/files/?path=Top%20stub%20dir/main.c&owner=auto HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1997, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1985, in wsgi_app
    response = self.handle_exception(e)
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1540, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/olmo/code/CodeGra.de/psef/auth.py", line 83, in wrapper
    return fn(*args, **kwargs)
  File "/home/olmo/code/CodeGra.de/psef/v1/submissions.py", line 659, in get_dir_contents
    found_file = work.search_file(path, exclude_owner)
  File "/home/olmo/code/CodeGra.de/psef/models.py", line 1472, in search_file
    File.is_directory == is_dir,
  File "/home/olmo/code/CodeGra.de/psef/helpers.py", line 249, in filter_single_or_404
    return t.cast(Y, _filter_or_404(model, False, criteria))
  File "/home/olmo/code/CodeGra.de/psef/helpers.py", line 206, in _filter_or_404
    obj = query.all() if get_all else query.one_or_none()
  File "/home/olmo/code/CodeGra.de/env/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2816, in one_or_none
    "Multiple rows were found for one_or_none()")
sqlalchemy.orm.exc.MultipleResultsFound: Multiple rows were found for one_or_none()