11i AP invoice accounting - where distributions are in different periods from header

Hi

can anyone tell me what set-up determines the GL account that will be used to ensure an invoice accounts properly to GL if there is a single header (liability) and multiple distributions in different periods. Theoretically this should not balance , so where does the balanced journal get its balancing account?  And how does the same work in future periods where there effectivly only a distribution and no liability?  I can't find anything in the user guide can help me.

Thanks

Linda