Hi,
That's normal and it's not something of HikaShop. The Joomla login system uses a cookie on your web browser to keep you logged in for the time of the session lifetime that you configured in the Joomla configuration, after which you're automatically logged out as the cookie expires.
There is no system to know when a tab/the browser is closed, which is why most login system work like this.
If you want to logout of your website before the cookie expire, simply click on the log out button of the Joomla login module (you can activate it via the Joomla modules manager). You can also create a new menu item of the type "user logout" to have a link of your menu where you can click to get logged out.