Hi Paul Mc,
According to the code you've posted, your page is in quirks mode, i.e. - it is missing a doctype definition, which is most probably the cause for the problem you are experiencing.
Our controls, as well as the entire ASP.NET AJAX framework are designed and developed to perform best in standards compliance mode, and it is recommended that the page is xhtml, unless quirks mode is required, for example - in old content management systems, where developers cannot add a doctype.
Please, add a valid DTD to your page, and if the problem persists, send us a sample project, along with your custom styles and layout so we can think of a solution.
Have a great weekend,
the Telerik team