Common Costs on CIP in Projects

We are using the common cost feature for asset creation in Projects.  We've chosen an allocation method of Current Cost so it spreads the amount to be allocated to each task based on the percentage of cost.  It works correctly on non-interfaced CIP, but does not recognize the amounts that have already been interfaced.  When late invoices come thru (after the asset has been placed in service) the common cost allocation does not allocate the new costs to the tasks based on current costs, but rather creates an "unassigned" line.  It appears to only calculate based on non-interfaced CIP. 

I have not been able to locate any documentation to show that "Current Cost" really means "Current non-interfaced CIP Cost".  Can anyone confirm that's what's happening and ideally produce documentation I can provide my users?  Or, am I missing something in setups that would allow us to include those costs?