The old cost engine is reportedly not working beyond Standard Costing. Its Average Costing. FIFO. LIFO has issues when handling corrections of posting dates and mistakes. The new Cost Engine from Libero solved those during tests as far as Average Invoice and Average PO is concerned. However its Standard Costing does not work. Neither is its FIFO/LIFO. Trackers reporting this has been posted to SourceForge. Please see Multiple Cost Methods cannot be active and FIFO cannot have starting zero Costs.
Verdict pending trackers status change: Libero Costing Engine is not backward compatible and breaks already working Standard Costing, FIFO and LIFO.