Updating migrated invoices, migrated Invoice Distribution Tax lines are automatically reversed and r

Hello All,

Has anyone been experiencing the issue below?

My currenct client had R12 Upgrade done 12-OCT-2014. The default migrated CA-Tax regime was ended on 11-OCT-2014. The client set up a total new Tax Regime. Since then , they have been experiencing an AP/TAX issue:

For ANY MIGRATED 11i invoices with migrated 11i Taxes,  once they are touched in R12 ( Basically anything which can trigger "Save" to happen and Invoice "Needs Revalidation",  for example, just adding 2 offset invoice lines WITHOUT selecting any Tax Classification Codes), the system will automatically reverse all migrated Invoice Distribution Tax Lines and regenerate new Invoice Distribution Tax lines for this invoice, and sometimes Amount Reversed <> Amount Regenrated.  Then the invoice became unbalanced and can not be revalidated.