When entering a Manual Sale Adjustment, there is a message at the top of the screen that indicates if the Sales Analysis will or will not be updated.
This is controlled by a setting in Admin / Defaults / Manage Product Defaults
If the Tick is removed, the Product Sales Analysis will Not be updated.
The adjustment never affects the Profit and Loss directly, it just makes the stock level go down, which would affect the stock valuation and therefore the cost of goods sold. BUT, your journal adjusting the purchase value cancels that out. See Updating the Stock Value to the General Ledger