Multiple nested resources with multiple methods are not displayed in Django Rest Framework Documentation

I wonder why Django REST Framework build-in documentation doesn't display methods for a User. I have only available list, create, read, update for these URLs:

url(r'^users$', views.UserList.as_view()),
url(r'^users/(?P<user_id>\w+)$', views.UserDetail.as_view()),

views.py:

@permission_classes([CustomPermission])
class UserList(GenericAPIView):

    """
    get: Return all users.
    post: Create a user.
    """

    serializer_class = UserSerializer

    def get(self, request):

        users = User.objects.all()
        serializer = UserSerializer(users, many=True)
        return Response(serializer.data)

    def post(self, request):
        serializer = UserSerializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)


@permission_classes([UserPermission])
class UserDetail(GenericAPIView):

    """
    get: Return user by ID.
    put: Update user by ID.
    delete: Delete user by ID.
    """

    serializer_class = UserSerializer

    def get(self, request, user_id):

        try:
            user = User.objects.get(id=user_id)
        except User.DoesNotExist:
            return Response(status=status.HTTP_404_NOT_FOUND)
        serializer = UserSerializer(user)
        return Response(serializer.data)

    def put(self, request, user_id):

        try:
            user = User.objects.get(id=user_id)
        except User.DoesNotExist:
            return Response(status=status.HTTP_404_NOT_FOUND)
        serializer = UserSerializer(user, data=request.data)
        if serializer.is_valid():
          serializer.save()
          return Response(serializer.data)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def delete(self, request, user_id):

        try:
            user = User.objects.get(id=user_id)
        except User.DoesNotExist:
            return Response(status=status.HTTP_404_NOT_FOUND)
        user.delete()
        return Response(status=status.HTTP_204_NO_CONTENT)

However example shown below is not visible in build-in documentation. I have also Swagger documentation in the project and everything is displayed properly.

urls.py:

url(r'^users/(?P<user_id>[0-9]+)/object$', views.UserObject.as_view()),

views.py:

@permission_classes([UserPermission])
class UserObject(GenericAPIView):

    """
    post: Create a user object by his ID.
    get: Return a user object by his ID.
    put: Update a user object by his ID.
    delete: Delete a user object by his ID.
    """

    serializer_class = ObjectSerializer

    def post(self, request, user_id):

        try:
            Object.objects.get(user=user_id)
            return Response(status=status.HTTP_403_FORBIDDEN)


        except Object.DoesNotExist:
            serializer = ObjectSerializer(data=request.data)
            serializer.fields['user'].required = False
            if serializer.is_valid():
                serializer.save(user_id=user_id)
                return Response(serializer.data, status=status.HTTP_201_CREATED)
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)


    def get(self, request, user_id):
        try:
            object = Object.objects.get(user=user_id)
        except Object.DoesNotExist:
            return Response(status=status.HTTP_404_NOT_FOUND)
        serializer = ObjectSerializer(object)
        return Response(serializer.data)

    def put(self, request, user_id):
        try:
            object = Object.objects.get(user=user_id)
        except Object.DoesNotExist:
            return Response(status=status.HTTP_404_NOT_FOUND)
        serializer = ObjectSerializer(object, data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def delete(self, request, user_id):
        try:
            object = Object.objects.get(user=user_id)
        except Object.DoesNotExist:
            return Response(status=status.HTTP_404_NOT_FOUND)
        object.delete()
        return Response(status=status.HTTP_204_NO_CONTENT)

There should be visible path users/{user_id}/object Any idea why is not?