Another bug or maybe just improper behavior. Recently Viewed module shows the product you are on as "recently viewed" at the time of viewing it. This should not happen when product has not been visited before - it is not recently viewed since you are visiting its page at the moment for first time and you are still on it.
I believe this exists in all XC versions since this module was introduced.
Bug report -
https://bt.x-cart.com/view.php?id=43391