Model backward inheritance in newforms admin

[occulkot@…]

class Document(models.Model):
    num = models.CharField(max_length=30)

class DocumentType(Document):
    payment_type = models.IntegerField()
    payment_date = models.DateField()
    client = models.ForeignKey(Client)

class OtherDocument(Document):
    first_field = models.CharField(max_length=111)
    second_field = models.CharField(max_length=123)

class DocumentRow(models.Model)
    document = models.ForeignKey(Document, related_name='rows')
    kind = models.CharField(max_length=30)
    date = models.DateField()

As you can see we have 2 kinds of documents - DocumentType and OtherDocument - every kind of document has same fields as "Document" and aditional fields. And every kind of document should hav rows.
It works perfectly in standard views but its problematic to implement in admin.
i tried

class DocumentRowAdmin(admin.TabularInline):
    extra = 10
    model = models.DocumentRow
    
class DocumentTypeAdmin(admin.ModelAdmin):
    inlines = [DocumentRowAdmin, ]

admin.register(models.DocumentType, PrzesuniecieAdmin)
admin.register(models.OtherDocument, PrzesuniecieAdmin)

And this way it only raises an exception about relationship.
Maybe some "inline_for_parent" option or sth?
im trying to make it working myself but im stuck in BaseModelFormSet.get_queryset method

[(none)]

Milestone post-1.0 deleted

[jkocherhans]

There are some typos in these models, but I did my best to re-create them, and they work with django trunk as of r10283. Please re-open with more details if this isn't fixed.