The version of the controls you are using is rather outdated. Moreover, note that the Classic controls are no longer supported and it is likely to see unexpected behavior when using them with modern browsers.
Please upgrade the controls to the latest release and see how they work for you. The current version of the components is 2016.3.914.
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Do you need help with upgrading your ASP.NET AJAX, WPF or WinForms projects? Check the Telerik API Analyzer
and share your thoughts.