Perhaps your last transaction was at zero?

If the WO-I Finished Production entry was made without proper costing (perhaps at standard before there was a standard defined) then the parts made would have gone into stock at $0 which in turn would result in shipment transactions at $0.  If the finished parts came out of the work order at $0, then the actual costs put into the work order would come out as WIP Variance whenthe WO is closed.