Great question — answering as the UphillTech team:
The problem is that when the country (Khu vực) is changed, not only the affiliate/register/country is triggered but also account/register/zone is registered and also for each such request the whole HTML page with loading of other JS and CSS resources is loaded via AJAX requests, which is really strange. Normally the JS and CSS resources should be cached within the browser so loading them per each request wouldn't be a problem, but as You could see within Your Firebug Console Tab, each JS resource has a timestampt hash within the URL, therefore it is really loaded each time. Since You cannot post the whole template and I do not see nothing wrong in the controller file posted nor JS within...
Full answer by shadyyx: https://stackoverflow.stackexchange.com/a/19125655 (CC BY-SA 3.0).
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