The Box under the Billable Column is Marked by Default When an Item is Added in a Purchase Order

The box under the Billable column will be marked by default when the following scenarios exist:

a. The Purchase Order transaction is created from a Sales Order.

b. The preference under Setup>Accounting > Accounting Preferences > Time & Expenses tab > Expenses: Items Billable by Default is enabled

The reason behind this behavior is because when Purchase Order transactions are created from Sales Orders (in the case of Drop Ship or Special Order transactions); the system presumes that the items in the Purchase Order are directly allocated to the Customer entity of the linked Sales Order which is why a customer entity is automatically specified when you try to subsequently add an item to the Purchase Order.

The Items Billable by Default preference will automatically enable the box under the Billable column for each line item added once a specific customer record is specified under Customer column of a purchase transaction.