Step workflow: prevent skipping ahead

-- HikaShop version -- : 2.3.5
-- Joomla version -- : 3.3.6
-- PHP version -- : 5.4
-- Browser(s) name and version -- : any
-- Error-message(debug-mod must be tuned on) -- : "Thank you for your purchase"

On the checkout workflow we have 3 steps plus the end enabled. The tabs at the top of the page showing each of the steps have links that can be clicked. This is great for being able to navigate backwards to previous steps, however this also allows the visitor to get ahead of the process.

On some occasions it bypasses the payment and terms of service acknowledgement altogether and just shows the final tab with the "Thank you" message, even though the order was not processed (see the attached image).

We have disabled SEF for the Hikashop component for testing, fearing that sh404sef was the problem, but in testing it still allows the visitor to skip ahead.

Is there any way to avoid this? Specifically the links in the tabs is nice, but maybe to disable the links on Tabs that should not be visited to prevent skipping to far ahead of the checkout process?

That works like a charm, thank you!