Purchasing/Incoming Product - Details is Done but Still Available

Hi sir, a 3 month old in ERP using Server 5.0.3 under ubuntu 8.0.4

The Problem is that afte PO is approved and incoming product is recieved all item details of the transaction is already done, but the transaction it self is status is still Available.
ex:
Referecnce: 40892 status: "Available" with 4 detail items all status "Available"
-after picking
- All 4 items is already set to "done" but the transaction master status is still available.

I have already seen few transaction of this issue on our server.
how is this possible?
how can it be prevented/fixed?
is there any patch for my version?
any remedy? what do i have to do?

Thanks in Advance.