Typically, when a purchase invoice is created at a price different from
the price at which the SVLs of the incoming picking were initially
created and confirmed, SVLs are generated to account for the price
difference. Once this happens, the invoice cannot normally be reverted
to draft due to stock_account restrictions.

Imagine international business settings where exchange rates are updated
daily; this limitation can be problematic. For example, if goods are
received on April 17th and the vendor bill is processed on April 18th
with a different exchange rate, an SVL record is generated, locking the
vendor bill. If a user then realizes a mistake, such as processing the
bill for the incorrect purchase order, they are unable to cancel it.
