Not able to update the rejected Work Confirmation

We are in the process of implementing Work Confirmation functionality. During testing, we find that application is not behaving properly when trying to update a WC which was rejected and trying to update. See below example.

PO line amount =1000 AED

Create a WC for 45% = 450 AED

Amount available (55%) =550 AED

Now create a WC for 15% (150 AED) and reject it. When trying to update this existing WC, system is showing balance remaining as 300 ie it is adding 150+550 and arriving at 700 instead it should keep the status as 550 and let me update with correct %.

Please advise if anyone has any insight into it.

Thanks, Vishal.