Inventory Valuation, Standard Cost and Cost Update Bug

I have been using this software for more than a year. However, there is a substantial flaw in design of the Inventory Movements. The software uses average cost method, but, there is standard cost method to transfer the cost of inventory sold to Cost of Goods Sold GL. This standard cost is ever fluctuating and often negative. How is this possible if costing method is average cost method is used? The software is a headache when there is high volume stock in and out. Especially when goods are returned, the cost of the returned goods is automatic and I dont know how the cost is calculated.

Secondly, the standard cost is frequently negative and the auto cost update is a headache because of lack of trail. Why the inventory valuation rate is different than standard cost? Is standard cost calculated based on average cost? If yes then when the standard cost is manually updated, should not it affect the inventory valuation?

Can someone explain in detail how the inventory costing can managed and how to stop cost update.

P.S. accounting norms does not allow cost updates. Can this be made optional in system settings ?