Hi Jimmy Yang,
There was a bug introduced in Q2 with the Windows7 theme. It is due to some negative margins in the template that messing up the header and resizers. This bug was fixed the next week after the Q2 release so the fix is available in the internal builds after that and also will be included in the service pack scheduled for next week.
We are sorry for the inconvenience caused. Let us know if you have further questions.
the Telerik team
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