Hi
TW is right. You have customer VOFM in requirements and formulas, so set a break-point and do debugging sessions. If you can, please, copy the coding and maybe somebody could help you. Check also the copy rules (as Lakshmipathi suggested) and how the system redetermines conditions. I suggest you read carefully SAP Note 24832 - Pricing rules / TVCPF. Perhaps the most important question is Q1.
I hope this helps you
Regards
Eduardo