The encountered behavior is due to the used version, since the release of the IE11 many incompatibility issues has been resolved. The matter was an ongoing task and using a more recent version of the Telerik UI for ASP.NET AJAX will include all possible fixes related to IE11.
Therefore, the official way to resolve this is by upgrading to the most recent version.
Alternatively, you should use the meta tag to force the IE11 to IE10 compatibility mode.
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