keep only cart session variables - clear ALL others

Good morning,
I have created a site with ecart and security assist.
I am debugging some issues.

The one that has me stumped right now is:

When I sign in, place order, update user record, then sign out, when i try and immediately order another product, one of my redirects on the checkout takes me to the wrong page. I have tested other scenarios and combinations of update/checkout/sign in/sign out and the problem only seems to occur when the criteria are followed.

I managed to solve the problem completely by changing my sign out page to kill ALL session variables (using your server behaviour), instead of just removing what I thought was everything, excluding the cart. (which I want kept intact on after signing out).

It's almost as if, there is a session being created on my update page (which uses an SA rule and redirect), which is surviving my sign out. Then, it is causing a redirect on my checkout.

To cut a long story short:

Do you know what the 'entity' is, that is surviving my sign out page, that would cause an incorrect redirect?

Thanks,

Ben