django model admin add form gets stuck

Consider this

@admin.register(Personal, site=admin_site)
class PersonalAdmin(admin.ModelAdmin):
    form = ChangePersonalForm
    add_form = AddPersonalForm

    def get_form(self, request, obj=None, **kwargs):
        if not obj:
            self.form = self.add_form

        return super(PersonalAdmin, self).get_form(request, obj, **kwargs)

The first time you try creating or changing an object, it will work fine. But, after you create the object, every time you try to change an object, you will get the add_form instead of the form

I fixed that by adding an else block

@admin.register(Personal, site=admin_site)
class PersonalAdmin(admin.ModelAdmin):
    change_form = ChangePersonalForm
    add_form = AddPersonalForm

    def get_form(self, request, obj=None, **kwargs):
        if not obj:
            self.form = self.add_form
        else:
            self.form = self.change_form

        return super(PersonalAdmin, self).get_form(request, obj, **kwargs)

As if there was some sort of class caching.

Anyone knows why?