Tax Transactions are calculating double

Hi,

I have a strange problem. When i register a transaction, i choose a memo line which has a tax classification selected, BUT, when i review the tax window, oracle has calculated Payables and Receivables Tax. A similar situation is happening in Purchasing, when i register a purchase requisition or a purchase order, when i click on tax manage web window, tax amount is calculated twice, Payables and Receivables. What's happening? What's wrong? 

Please help me, is very strange.

Thank you.