WIP Value report: How is Material cost calculated?

The 'Material' column on the WIP Value report represents the cost of the material that has been issued into the Job.  Job Issue transactions always occur that the item's Inventory Cost *at the time the issue occurred*.  Job Estimated Cost is irrelevant in material issuing.  To see a history of cost transactions for an item, you can go to (Inventory > Data Views > Inventory Transactions Detail).