Editing a model that contains m2m inline hangs the server

[v.kryachko@…]

The code first:

#models.py
class Obj(models.Model):
    name = models.CharField(max_length=100)

class ObjConf(models.Model):
    obj = models.ForeignKey(Obj, unique=True)

    someStuff = models.ManyToManyField('someStuff')

class someStuff(models.Model):
    name = models.CharField(max_length=100)

#admin.py
class ObjConfInline(admin.TabularInline):
    model = ObjConf

class ObjAdmin(admin.ModelAdmin):
    inlines = [ObjConfInline,]

admin.site.register(Obj, ObjAdmin)

When I create a new instance of Obj, everything is OK. But when trying to /admin/project/app_name/Obj/1 the server starts thinking forever and never responds(only Ctrl+C works)