Automatic posting in MM for Invoices

Hello all

I'm having an issue: This scenario is in Argentina so local currency is ARS and foreign currency USD. Company Code uses PO in USD currency because of material.

Then invoice receive is posted in local currency (ARS) and after that goods receipt is posted in USD. In many cases exchange rate differences are posted to the stock gl account (BSX) in MIRO.

In other cases, differences are posted to price differences directly in profit account (KDM PRD) in MIGO.

How is currency choosen?

Both scenarios occurs with same vendor, same material, and PO conditions.

My main question is if exists any exists any reason for this, I mean, to post to profit/loss account or stock account.

Thanks