When Work Order Completion with Backflush is created, the system combines the effect of a Work Order Issue and Work Order Completion. Only a Work Order Completion Transaction will be created but the GL Impact will include that of the Work Order Issue.
When Work Order Issue is already created, and you attempt to create a Work Order Completion with backflush, you will not be allowed to save the Work Order Completion with backflush since you will be required to enter component quantities. There will be an error "Quantity must be greater than zero for at least one of the component items." Component quantities default to zero since the committed quantities for this component has already been issued. This behavior is only true when MANUFACTURING ISSUE BASED ON COMMITMENT Accounting Preference (Setup > Accounting > Accounting Preferences > Order Management) is set to Limit To Committed or if MANUFACTURING ISSUE BASED ON COMMITMENT is set to Ignore Commitment but ALLOW OVERAGE ON WORK ORDER TRANSACTIONS is disabled.