I tested the scenario that you describe with IE7,8 and 9, FireFox and Chome and I am not able to reproduce the issue in none of the browsers (see the attached image). Therefore I can only guess, in case you are using a custom skin, that some of the applied styles are causing this appearance. Can you please provide a live url where we can inspect it locally or send us a support ticket with a simplified runnable project that we test and help you out with a suitable solution?
the Telerik team
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