Allow non-GL changes in closed period

NS folks.....clarification, please..... what is the expected result if you have these settings:

1) CHECKED:  "Allow Non-GL Changes" for a closed period (Setup > Accounting > Manage Accounting Periods > select accounting period)

2) NOT checked: "Allow Admins to Post in Closed Periods" (Setup > Accounting > Accounting Preferences > General > General Ledger)

I entered a case (716143) when I found that I could make a non-GL change on invoices, but could not make a non-GL change on an Item Fulfillment (error: "You cannot change the G/L impact of a transaction in a closed period").  I thought that the problem was with the Item Fulfillment, but support is telling me that the actual problem is that it shouldn't have let me make the non-GL change on the invoice.  Okay, that's fine, but