Pay item 002 in customer ledger

Dear All

There is Credit order Document type RM, its order has got three lines ( 25+5+2.5) put together quantity of  32.5 with total value of $2500. it is formed pay item 001 with value of $2500  and due date as G/L date.  But there is second pay item 002 line also generated with no value with due date as per customer pay terms means G/L date+ defined pay terms. i failed to understand  Why this line got generated at all.

Thanks/RAO