One pick slip number generated for two different shipment numbers

We are trying to understand the behavior of the system, why one pick slip is generated for two different shipment numbers.

Please find the pickslip grouping rule

 

Sharing the example data, not displaying the actual customer data

Sales order-1

Customer - ABC

Item - 45671

Shipping Method -Fedex

Sales order-2

Customer - ABC

Item - 45671

Shipping Method -UPS

Pick Slip Number for both the order is 8901

Shipment

Sales Order-1 -456789

Sales Order-2 -456800

Why one pick slip number created with two different shipments? How can we create one pick slipper shipment?