I have two models:

class Course(models.Model):
    name = models.CharField(max_length=255)

class Teacher(models.Model):
    name = models.CharField(max_length=255)
    courses = models.ManyToManyField('schools.Course')

The serializer are:

class CourseSerializer(serializers.ModelSerializer):
    teacher_set = serializers.PrimaryKeyRelatedField(many=True)
    class Meta:
        model = Course

class TeacherSerializer(serializers.ModelSerializer):
    class Meta:
        model = Teacher

and the views for courses and teachers:

class TeacherViewSet(ModelViewSet):
    serializer_class = TeacherSerializer
    queryset = Teacher.objects.all()
    filter_backends = (filters.DjangoFilterBackend,)
    filter_fields = ('courses',)

class CourseViewSet(StaffRequiredMixin, ModelViewSet):
    serializer_class = CourseSerializer
    queryset = Course.objects.all()

After I create a course and a teacher, when I am adding the teacher to that course and do get list of teachers, it is returning me two exactly same teacher objects.
I found that is because filter in the TeacherViewSet. If I remove filter, it is giving me correct result. I was using django-filter version 0.7. When I changed to django-filter version 0.5.4. It is working fine then.
Is that a bug of version 0.7?

Edit:

What I did was:
I created two courses (c1 and c2), then created a teacher (t1). Then I added t1 into c1. When do GET /api/teachers, I get t1 object, that's right. If add t1 into c2 and GET /api/teachers again, I will get two t1 objects.

That won't happen if I put in OrderingFilter and set ordering

I am not a native English speaker, and the question I posted was not that clear. Hopefully this update can make more sense