Pay Status for invoices created with zero amount?

I just read E1: 03B: Invoices Created with Zero or Blank Open Amounts Assigned a Pay Status of P vs A by the Invoice Entry Master Business Function (P03B0011/B03B0011) (Doc ID 1632858.1), which states "In 9.1 the code for Bug 18145982 incorrectly changed the logic in the Invoice Entry MBF to assign pay status P to zero amount invoice pay items." and "Accounts Receivable invoice pay items (F03B11 records) created with a zero, or blank, open amount should be assigned a pay status of A."

Could you please help me to understand why it is incorrect for zero value invoices to automatically be created with a pay status of P?