Invoice Issue

Hi Gurus,

I am doing a PO, say 36000rs for 100 KG materials with a tax amount of 720 rs. So while doing GRN, the accounting document will be as, Material account 36720rs debit and GR/IR account 36720rs credit. While doing invoice, i am changing the Tax code (which is 0%). Normally the accounting document should be as, 36000rs to vendor account, 36720rs to GR/IR Account and balance 720rs to material account. But this 720rs is going to two accounts. i.e 560rs to Material account and 160rs to Cost difference account. Why is it happening like this. No other issues are there in Calculation schema or condition types. Can anyone help me out.

Thanks and regards,

RP