Problem with partial delivery

Hello all. I have been playing around with the accounting software and so far I am extremely impressed. I have however run into some difficulty and not sure if its me or if its a bug, but I can repeatedly duplicate it.

I make an inventory item, call it item A. I then create a Sales Order Entry for a customer with a particular quantity of item A, say for example 10. Item goes on back order as expected. I then create a Purchase Order Entry, Receive Purchase Order Items, and as expected, the inventory updated to now show the items in stock. From here is where something interesting begins to happen.

1). If I attempt to make Delivery Against Sales Orders for the full amount (all 10 of item A), I can process dispatch no problem.

2). If I attempt to make Delivery Against Sales Orders as a partial delivery (say 5 instead of all 10), I can process dispatch again, no problem. HOWEVER, if I attempt a second delivery against the same order for the remainder of the items (5 remainder in my case), it automatically shows I have delivered before, and shows the number I need to deliver to complete, BUT when I hit Process Dispatch, i get the following error:

"This document cannot be processed because there is insufficient quantity for: [Item Code]"

This only happens on partial delivery. I have verified that the inventory items are on hand by pulling up a report, but the system just does not want to complete the delivery. Can anyone else duplicate this problem or is my installation bugged?

Thanks in advance.

Denis.