Such an old version of our controls should be expected to have problems in modern browsers (IE, Edge, the current Firefox and Chrome).
Each release of ours only supports browsers that have been around at the time we shipped it. In this case the 2012 release will support IE10 at most.
New browser releases tend to bring breaking changes (like the event handling issue in IE11 you have noticed).
My best advise is to upgrade to the latest to get support for the current browsers, including mobile ones: http://www.telerik.com/aspnet-ajax/tech-sheets/browser-support.
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