2. please see above my question.
3 & 4. I tried disable module and plugin (eg, joomfish, redirect registration joomla to Hikashop, all no result.
But, a correction here, found the system actually not kick out the user when user click on any radio button (select shipping method, payment method or select shipping address), or either next button and add coupon button. It's direct to homepage, when user click on "my account" link (at top of search field, the middle one) and logged in again, the item is still remain in the cart.
From back end, can see user still not logged out, so is logged in twice or 3 times..
I have a logout menu on the right column (on top of shopping cart module), only after logged in can see. If user logged in from "my account" (on top middle link above search field), can see this logout menu. But, if user add to cart and proceed to checkout, and prompt to log in, will not see this logout menu?
I am very confuse now!!
Thank you!