STO is created, it creates 2 Deliveries for a single STO

I saw from my client's production system for one STO system has created two Outbound deliveries. upon further checking in first OBD they have combined both PO lines where as in second OBD it has added second line item of PO, both OBDs are created by the system no human intervention, however i check that the shipping conditions are looking different in both line items, both line delivery dates are same. in the first OBD it has picked both PO lines with full quantity and delivery process is completed where as in the second OBD its status is in 'A' not yet processed. Please help.

Thanks.