That is similar to the problem I am having. And I must confess to being as confused as Laura is. Each time you print the item valuation report and back date it certain items change for either quantity or average value.

Does changing the stocking unit or category of an item affect the costing. I have one item which has materially changed from an average cost of $2.46 a lb to a negative cost. I have checked all the receipts and adjustments and they were done at the correct cost. The only change I can see is that the category has changed.
Another item costing unit was changed from case to each. The first report gave me a value of $1,660 per case, but the second report is giving me the correct value of $33.46 a case. The actual cost works out correctly.