Magento1.7: shopping cart problem

In Magento I ran into some important issue:
When I logged in and added some products to the cart and logged out, logged in again, then these products were still in the shopping cart.

----> This shouldn't have happened because I installed "Clear Persistence on Log Out".

In this case, the following steps are performed:

• I entered.
• Added 2 items to cart.
• Now I am logged out.
• Then, without logging in, I browsed the website and added 4 products to my cart.
• After that, during the check, I was prompted to log in, so I logged in.
• Now instead of 4 products (which are intended), I see 2 + 4 = 6 products in my cart at the time of checkout.

I configure it as shown below:

• Enable Save - Yes
• Service life (in seconds) - 60
• Enable "Remember me" - Yes
• "Remember me" Default value --- No
• Clear Save On Logout - Yes
• Save shopping cart - Yes

But I am not able to understand the problem, in the configuration I set 60 seconds. I logged out and after 5 minutes I logged in again. I found that products remain in the basket.

The product is configured to be removed from the shopping cart after logging out.

I messed up this issue. Please help me.