Negative price of goods in MIGO

When I try to do MIGO I get an error "M7 330 Price of goods mvt will become negative"

Looking at PO History I notice there was a 101 and 102 for the same quantity but that ended up with different value, so that seems to be the reason of this wrong valuation. I have not found the reason for this.

For what I have read:

a) it could be fixed if I do an invoice for a greater quantity, do the GR and after that cancel the invoice.

b) i should not just change the message to warning in OMCQ since negative movements of stock should not happen

How should I tackle this problem?

Regards,

Carlos