Select Cash Receipts Invoices Screen

We recently upgraded from 4.10 to 4.50.  In our old version of MAS-90, The INV AMOUNT field would remain static no matter how much money was posted against it.  However, in our new  version, when funds are posted, the INV AMOUNT will go to zero. 

 

Is this just a difference in versions, or do we need to apply a fix for this?

Thanks!