When cancel an invoice, it didn't pick up the Tax line

Hi Gurus,

When I were cancelling an PA customer invoice (with tax amount), the credit memo didn't pick up the tax line. It only credited the revenue line.

After it interfaced to Accounts Receivable, the Credit memo only credit the revenue line despite there is tax oustanding amount for the original invoice.

Is it intended fuctionality?

Thanks,

Faye