Accounting for Voucher and Payment

Hi All,
We have budgeting implemented and when we create the PO and for that PO we create the Invoice/Voucher and then Payment the accounting which is coming is really not understable. So please help me to understand that from where these accounts are defaulted : on Voucher


and on Payment it is showing like this:



Here why these InterE Pay - AP and InterE Rec - AP accounts are defaulting and from where they are coming.



Thanks in Advance...