如何使用 unique_together 建立抽象模型？

为什么我得到：

Error: One or more models did not validate:
test.test: "unique_together" refers to slug. This is not
in the same model as the unique_together statement.
test.test: "unique_together" refers to version. This is not
in the same model as the unique_together statement.

我有这样的模型定义：

class SlugVersion(models.Model):
    class Meta:
        abstract = True
        unique_together = (('slug', 'version'),)

    slug = models.CharField(db_index=True, max_length=10, editable=False)
    version = models.IntegerField(db_index=True, editable=False)

class Base(SlugVersion):
    name = models.CharField(max_length=10)

class Test(Base):
    test = models.IntegerField()

我有 Django 1.3。

看来这是一个bug https://code.djangoproject.com/ticket/16732在姜戈.