Please, check your page's DOCTYPE declaration, as the issue might be caused by the lack of a DTD (quirks mode) or a DOCTYPE different than xhtml (for example HTML 4). All RadControls for ASP.NET AJAX are intended to work under standards compliance mode.
Another possible cause for the issue might be the inheritance of global CSS styles (table, tr or td), so please, do the following test - remove your styles from the page and reload it.
If the issue still persists, open a new support ticket and send me a sample project that demonstrates the issue and specify with which browser and version in is observed.
the Telerik team