I created a demo database on odoo.com with eCommerce app and here is my config:

-2 company:

    - company A has website A

    - company B has website B

When I go to the website front-end of website A (logged in by default admin account), I add some product to my cart. Then I switch to website B (which I haven't logged in before). However, in website B, I already have some products in my cart (which exactly the same like my cart in website A). Is this a default flow in Odoo? Can anyone explain me why it is.

Moreover, when I log out my account, and go to my domain my-demo.odoo.com, there is no way to choose the website which I want to access. I know that there is the config of website domain in backend but currently I dont have any domain on hand, How can I test the performance and flow of multi website in multicompany environment? Is there any suggestion?