SAP Functional, Basis and ABAP Programming Reference Books
SAP Billing - Combine Billing for deliveries with different date

When using transaction VF04 or Billing (background), the date of the billing document (e.g. the current date) must be entered (In VF04 : settings, default data.)

In VF06 or background: variant with parametrization) to avoid an unwanted split due to the billing date.

This OSS notes is very helpful :-

11162 - Invoice split criteria in billing document

36832 - Invoice split in fields from the sales order
 

Best regards,
SAP Basis, ABAP Programming and Other IMG Stuff
http://www.sap-img.com