Fulfillment serials not matching serials on Invoices

I am reconciling inventory, and have some major issues here.  For example, I have an SO with qty 5 on one line.  The fulfillment shows 5 serials being shipped.  The invoice lists 5 serials.  The sales order was fulfilled, and does not show editing, the invoice was created 2 hours later, never edited, yet only 4 of the 5 serials match on fulfillment vs invoice.

What is going on here??  how can this happen?  this was not a special order.  We do use auto commit, but have the ability to override commitments.  Is the invoice possibly picking up an original commitment serial?