Finally closed PO line amount still in PO header total

Functional user is asking why the amount of a finally closed PO line is still included in the PO total in the header.  If a line is cancelled, the line is reduced to the already matched amount and the PO total is reduced.  Since Finally Closed lines cannot be reopened, why does the total remain the same? 

Example: PO for $100 - 2 lines of $50 each.  Cancel line 1, then po header shows Po total = $50.  But if you Finally close the line, it cannot be used, but the PO total still shows $100.

Do others cancel first and then finally close to eliminate this issue?