purchase vendor invoice not balanced: with "Purchase expenditure for product" and "Purchase expenditure , Un-invoiced" having balance

Dear 

when i receive a PO i am getting the below which is fine

Purchase Accrual           Credit    $30

Product Receipt             Debit     $30

but i am invoicing a that purchase order but i am getting the below result 

Purchase expenditure for product      Debit $30

Purchase expenditure , Un-invoiced   Credit $30

Purchase Accrual                                 Debit $30

apparently something is wrong, no "vendor balance" and the entry is not balanced 

it was working fine before , i am trying to track what could have changed