django.db.utils.ProgrammingError in Django 1.7.6

[martin-c]

From models.py:

from django.db import models
from modelmixins import ModelMixin


class AMixin(ModelMixin):
    field_from_a = models.CharField(max_length=32)


class BMixin(ModelMixin):
    field_from_b = models.CharField(max_length=32)


class MyModel(AMixin, BMixin, models.Model):
    my_model_field = models.IntegerField(default=42)

Created initial migration using python manage.py makemigrations foo,
then 0001_initial.py shows:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import models, migrations
import foo.models


class Migration(migrations.Migration):

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='MyModel',
            fields=[
                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
                ('field_from_a', models.CharField(max_length=32)),
                ('field_from_b', models.CharField(max_length=32)),
                ('my_model_field', models.IntegerField(default=42)),
            ],
            options={
            },
            bases=(foo.models.AMixin, foo.models.BMixin, models.Model),
        ),
    ]

So far, so good.
Next, python manage.py migrate,
Result:

Running migrations:
  Applying foo.0001_initial...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "***/.python-env/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "***/.python-env/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "***/.python-env/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "***/.python-env/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "***/.python-env/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 161, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "***/.python-env/lib/python2.7/site-packages/django/db/migrations/executor.py", line 68, in migrate
    self.apply_migration(migration, fake=fake)
  File "***/.python-env/lib/python2.7/site-packages/django/db/migrations/executor.py", line 102, in apply_migration
    migration.apply(project_state, schema_editor)
  File "***/.python-env/lib/python2.7/site-packages/django/db/migrations/migration.py", line 108, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "***/.python-env/lib/python2.7/site-packages/django/db/migrations/operations/models.py", line 36, in database_forwards
    schema_editor.create_model(model)
  File "***/.python-env/lib/python2.7/site-packages/django/db/backends/schema.py", line 262, in create_model
    self.execute(sql, params)
  File "***/.python-env/lib/python2.7/site-packages/django/db/backends/schema.py", line 103, in execute
    cursor.execute(sql, params)
  File "***/.python-env/lib/python2.7/site-packages/django/db/backends/utils.py", line 81, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "***/.python-env/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "***/.python-env/lib/python2.7/site-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "***/ctsweb/.python-env/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: column "field_from_a" specified more than once

where *** is the project path.

Any ideas what is going on? If I comment out the fields contributed from AMixin and BMixin in 0001_initial.py, then the migration runs without error and the db tables are correct.