What’s a bit odd is that on his inventory Item screen he shows
Item code, Item Name, Unit Name, Qty on Hand, Average Cost and Value
whereas the current version shows
Item code, Item Name, Unit Name, Qty to Receive, Qty on Hand, Qty Owned, Average Cost and Value
I now understand what is happening. I can duplicate the behavior.
@WAQASKHAN, you did not set up this inventory item to track quantity to receive. However, you entered a goods receipt for it. Therefore, Manager adjusted the quantity based on the goods receipt, then immediately reversed the adjustment (automatically).
The ability to track or not track receipt and delivery of inventory items was only added to the program a few days ago. Formerly, if you enabled the Goods Receipts or Delivery Notes tabs, they applied to all inventory items. Now, they are selective. Since you did not designate this inventory item to be tracked, you should not enter goods receipts when you purchase it. On the other hand, if you want to track its delivery and continue using goods receipts, you must edit the inventory item definition and check the box.
I had not had time to experiment with this new feature yet, so did not fully understand it. I had expected the program to reject the goods receipt. Instead, it accepts it and immediately reverses it. One advantage of this approach is that your personnel do not need to know or remember which inventory items are being tracked by goods receipts and which are not. They can enter goods receipts for all items. But when an item is not set up to have its quantity to be received tracked, the end result will be that the program considers it to be on hand as soon as the purchase invoice is entered.
I get all sorts of discrepancies if I enter a GRN for an item not tracked by quantity
Sometimes it posts a + and a - qty
Sometimes it doesn’t - seems to be connected to using or not of an inventory location, or go back and change the inventory location, it adjusts one leg and not the other
Looks like a case of procedural discipline being required when using this feature 
Hmmm. Interesting. I happened to test in a business with inventory locations, but did not explore behaviors when changing them. This calls for more research. There may be something wrong buried down deep.
I think it was when I added the GRN without specifying a location, the plus and minus were added to the unspecified location.
If you then change the location to a valid location, only the plus gets moved and the minus stays where it was.
Presumably if I specified a location and then changed it the same would happen