How to reinitialize jQuery unobtrusive validation?
To parse the form's validation attributes after you return it to the page you need to run this: $.validator.unobtrusive.parse('#yourFormSelector')
In my application I put this call into the ajaxComplete handler so I don't have to worry about it anymore. I have it reparse every form on the page and it's been working fine in production for quite a while (even when there are a couple hundred forms on the page).
$(document).ajaxComplete(function() {
$.validator.unobtrusive.parse('form');
});