I checked this bug on http://demo.opensourcecms.com/zencart

If you have only 1 method available for Shipping, in my case "Store Pickup - Walk In", this only option available will NOT be automatically be selected. The customer has to click by himself on "store pickup", even if this is the only option available.

If this option is not selected by the customer, the same page keep loading up, but no error message is displayed.

sanji