Why won’t a custom jQuery Validation method run on an input element using KendoUI?

In our web application, forms are generated by ASP.NET MVC, which uses jQuery Validation and Unobtrusive Validation. I was recently working on a form we use in our own web application, and we planned to integrate on an external website via AJAX. There is a select menu in the form that allows the user to select from a list of items, and it has KendoUI’s MultiSelect plugin applied to it. The form worked just fine when used on our primary site, but when I used this form on an external site (making sure to include all necessary JavaScript), a custom validation method we add on page load to that one select menu absolutely would not run. Can you guess what caused this?