• This “issue” (not being able to change standard costs directly in Item Maintenance) was introduced in v4.40 when we re-wrote the Inventory module but it’s not a defect, it was a correction.
• This should have never been allowed in the first place
• If costs need to be changed frequently, they are not ‘standard’ costs
• When the standard cost is changed; it revalues the entire inventory of that item and since inventory is an asset you have just revalued the equity of your company
• Therefore, GL must be updated AND people have to be out of the system to post to GL
• Prior to v4.40 the standard cost could be change in Item Maintenance. Orders could then be processed with the new cost before the GL had been updated and the inventory balances would no longer reconcile to the GL balances. 
• This was problem prior to 4.40 but a lot of people simply never reconciled the trial balances or they would do some kind of adjustment.
  

Please consult a tax advisor or reseller to discuss the best costing method options for your companies business needs.