1. Sales Invoices do not follow automatic numbering after a new invoice sequence have been started. It just follows the old sequence.
In the above example, invoice dated 12th July has been manually started as Invoice number 1.
The next invoice is supposed to automatically number the invoice as 2 but instead is following the earlier sequence.
2. Balance due is not calculated wrt the customer but only wrt the particular invoice.
Here the balance due is 1000. When another invoice is made to the same customer, this balance due amount is supposed to add with the new invoice total. But instead it just shows the total of that invoice.
NOTE: The default plain theme is used everywhere. The invoices have been created in order and not edited and updated.