Closed Purchase Order> Status is Set as 'Billed' rather than 'Closed'

For instances wherein a Purchase Order that was Closed has the status automatically set to 'Billed' instead of 'Closed', this is for the following reasons:

1. The Purchase Order only has an Expense line item under the Expenses tab and that there are no Items on the Items tab and;

2. On the Expense line, the Closed checkbox is marked.