R42800 (P03B0011) Sales Update splitting F03B11 into multiple pay items.(+/-)

We have a sales order/invoice with positive valued stock item lines and negative value promo code lines.
Sometimes when running R42800 Sales Update it splits the F03B11 into two pay items.
001 for the positive value lines with due date = terms.
002 for the promo code lines with due date = current date.
P03B0011 PO #5 Credit Memo Due Date is set to blank = "Use G/L date as due date".

Should this really effect invoices (not credit memo) docs and why does it only seem to happen on some orders?

E1 9.1 tools 9.1.3