Tax exemption removal on Customer

Hi,

In our set up ,we have some Customers which have 100% tax assumption for certain tax codes.

The status of the exemption is Unapproved. When I am creating invoice thru Auto invoice ,Tax is not coming to invoice.Which means it is considering the tax exemption.

If i am putting an end date to the unapproved exemption.And try running Autoinvoice again,I can see new entires in the Exemption Window having Unapproved status.

I would like to understand the unapproved status of exemption.Whether Receivables considers this kind of exemption.Because I tried with two transactions .In one i got to see receivable is considering it..In another it is not taking into account.Kindly suggest,how to remove Tax exemption for the Customer.