Can't Delete Items from Shopping Cart

Running: v1.3.9h

Software was upgraded from a much earlier version (about 4 years old, but don't recall the version).

Here's the problem -

Customers can add items to their shopping carts. But checking the box in the "Remove" column and clicking the Update button does NOT remove items from the cart. Anybody else have this problem?

Software was upgraded from a much earlier version
Guessing because you did not provide any more information that your upgrade was not complete or done properly

Actually, that's not the case. The upgrade has been running fine in most regards for at least six months. My customer just became aware of the cart issue. It might have been doing it all along since the upgrade, and it might not.

But just because I'm not sure of the version that was upgraded from (we host a lot of stores), or the date it happened, it has to be a faulty upgrade?

Is anyone willing to help with this issue aside from telling me the upgrade was bad? Is there something else I can check?

Backup your copy of includes/templates/YOUR_TEMPLATE/tpl_shopping_cart_default.php, then restore a new copy from a fresh download of 1.3.9h. Retest.

If it still fails, backup a copy of includes/modules/pages/shopping_cart (directory), then restore a new copy from a fresh download of 1.3.9h. Retest.

Likely one of these two places was done incorrectly during upgrade.