Hi,
What you're describing is typical of someone deleting orders in the hikashop_order table without deleting the links to the products in the hikashop_order_product table in the database.
Then, the auto increment is reset to the highest order id remaining in the hikashop_order table, and next time an order is created with the id of a previous order, the products from the deleted order with the same id will be seen by HikaShop as linked to the new order.
The proof of that is that the grand total is calculated by HikaShop just before the order is created by HikaShop, while the subtotal is calculated dynamically when the order details is being displayed, which explains the inconsistency between the two amounts.
So updating won't change anything to that and there is no bug. The issue is that previous orders were not deleted properly by the person who did that. Normally, when you delete an order using the delete button of the orders listing, it will delete both the order and the link with the products so that this cannot happen.