Possible Resolution:
There are several scenarios where purchase order receipts post to the PO Variance Adjustment account:

1. Receipt of Good post to the PO Variance Adjustment account when an item is valued at standard cost and is received at a cost other than the standard cost. Inventory will only be valued at the standard cost. The difference will post to the purchase variance account.
2. If the item has an average cost valuation method and the item has a negative on-hand quantity at the time the ROG/ROI is updated. Run an Inventory Detail Transaction Report for one of the items in question. Use a date range of 01/01/1900 through 12/31/9999. You should see the PZ transaction which was created at the time of the PO variance. Above that, there should be another transaction with a similar dollar amount. This transaction could have a source of SI, BI, SO....To avoid these PO variances on average cost items, do not let your inventory go to a negative quantity on-hand.
3. Receipt of Goods or Receipt of Invoice will post to the PO Variance Adjustment account if there is a difference between Receipt of Good and Receipt of Invoice. Inventory will be valued at the cost of the Receipt of Goods. When the item is invoiced to relive the Purchase Clearing account, the difference between the cost will post to the PO Variance Adjustment account.
4. Multiple partial Receipts for the item on the Purchase Order with variable unit costs. Example: Receipt 1 unit cost is $1.50 and Receipt 2 Unit Cost is $1.00. The Extended Cost of each receipt is averaged to arrive at a Unit Cost for the Purchase Order. The difference between the Unit Cost of the item being received and the calculated unit cost will post to the variance account.

Note: The PO Variance Adjustment account is defined in Product Line Maintenance.