Billing Documents Printed Randomly

Dear All,

We have a strange issue, where through Billing Background job -Billing Documents are printed randomly e.g. Billing documents will be Printed at Printer in this sequence--- Billing Document - 1,2,3,6,7,4,8,9,5 etc etc...

How to fix this.

Any help/clue on the same would be appreciated.

Regards,

Vikas