All versions of Telerik UI for ASP.NET AJAX support only the native rendering mode of Internet Explorer.
The compatibility mode of IE is officially not supported as noted in the Browser Support page
, because it forces the browser to render the page in IE7 emulation mode. IE7 is no longer supported by Microsoft and does not work with CSS3, which is widely used by the lightweight rendering of the Telerik AJAX components.
That's why my advice is to disable the compatibility mode
. The following meta tag could be useful too:
<meta http-equiv="X-UA-Compatible" content="IE=edge" />