I tested using the markup you sent, but I was not able to reproduce the issue. I took a screen-shot
showing how the page is displayed at my side in Firefox browser(I tested with 2015.2.623 version of Telerik UI for ASP.NET AJAX).
Attached you may find the project I tested with. Please inspect it at your side and modify it in order to show me what I am missing to reproduce the problem.
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