SOAP: Why Customers balance is 0 after successful creating and booking invoice?

Hello,

I create invoice with CurrentInvoice_CreateFromDataArray

I add some lines to invoice with CurrentInvoiceLine_CreateFromDataArray

I book invoice with CurrentInvoice_Book

But customer's Balance stays 0.00 ( I need it to be  -1242,35 )

Please see this screenshot for clarification

http://lowntech.com/Why_Balance_is_zero.png

See? for some reason system creates 2 entries, so final balance is zero, why there are 2 entries?

How can I change customer's balance with SOAP, via creating and booking invoice? What am I doing wrong?

Thanks,

Natasha