Expenses 'Post Payments' Process creating reverse accounting entries

I'm implementing PS Expenses 9.1 for the first time and am confused by the accounting entries resulting from expenses' processing.  So let me explain what I'm seeing and perhaps others can fill in any obvious gaps.

1. Expense Reports are created and approved. 

2. Stage Payments and Publish to Payroll are run.    

3. Post Liabilities is run; from EX_ACCTG_LINE, expense accounts on the EX_LINE_DIST are debited; the pre-defined liability account receives an offsetting credit.  An expenses journal is created reflecting this information.

4. Payroll completes their processing, runs PAY_GL01, messages are returned and an AE updates EX_SHEET_PYMNT, allowing Post Payments to be run.  HR_ACCTG_LINE is populated with the expense debits and payment account credits for Payroll journal creation.