# Tuesday, June 9, 2015¶

Fixed some documentation problems.

Still working on the novat branch (ticket #294). Here is a funny problem over which I stumbled:

• Sequenced defines a field seqno and is abstract base for VoucherItem
• VoucherItem is abstract base for both AccountInvoiceItem and VatItemBase (both of which are themselves abstract models).
• And now InvoiceItem inherits from AccountInvoiceItem and VatItemBase.

That should be fine, shouldn’t it? Even Django says that it is valid (manage.py validate).

But when I try to initialize a database which uses lino.modlib.vat, I get:

OperationalError: duplicate column name: seqno


This is due to a known bug in Django: Django ticket #19465.