Hi Pravin
In the old thread below you will find the details of how to handle invoice splits.
http://scn.sap.com/thread/2038739
Basically as the system generates the billing document it first does the header and then
each item in turn. Some of the data from each item (See 11162) is transferred to the header
As there is only one header field if there is a difference at all in respect of any of the fields
outlined in the note. It will cause a split.
The way to avoid the split is to either set a common value using the item data transfer routine
or to clear the values that are causing the split.
Hope it helps you further
Kind regards
Brian