Incorrect financial records created for certain event payments

The issue is that incorrect financial records are generated when a back-office user updates a "pay later" event contribution record with less than the full amount expected. In this situation, the sum of "civicrm_line_item.line_total" does NOT match the number in "civicrm_contribution.total_amount". Since the detail about the various financial types in use are in the line item table, its impossible to get an accurate report on how much was actually received for each financial type/line item.

To reproduce:

1) Create a paid event that uses a price set with a variety of financial types. Configure the event to allow "Pay later" registrations.

2) Register a participant for this event: be sure to select various price set options that use different financial types; Also choose "Pay Later" (This can be done via the online event page or via the backoffice area) ( For this example I assume the grand total is $100 )

3) In the back-office area, click the "edit" link for the contribution that got created in step 2 above.

4) Change the contribution amount to $50. and change the status to "completed"

At this point the sum of "civicrm_line_item.line_total" is still $100, yet the "civicrm_contribution.total_amount" is $50.

My thoughts is that either a) The correct records should get created/updated OR b) Do not allow the end-user to change the contribution amount when editing this record.