How to trace difference on Stock Entry: Manufacture

Hi everyone:

I’m trying to identify the cause of an unexpected valuation difference in a production.

We have create a Stock Entry of type Manufacture to reflect the production of 5 items.

There are only “source items” and no additional costs.

I have been explained by our accountant that in this case, the operation should be reflected on the accounting books as crediting the value of the items from the “parts inventory account” and debiting the same value on the “finished inventory account”.

However, we are also getting an unexpected difference as shown on the image below:

We would like to trace the reason of that difference. I guess we can take every “source item” on the General Ledger and check their history. However that would be quite consuming in this case as there are about 53 items.

What would be the correct procedure to identify the cause of that unexpected difference?