Hello Shin Tei,
Please, find below my answer, provided in the support ticket you have started:
This is a known issue in Internet Explorer with relatively positioned content within a scrollable container. You can find a demonstration here (check the page with IE6/7 and then with Firefox to see the difference). The fix would be to set "position:relative" to the container, in this case this is the panel:
<asp:Panel ID="Panel1" runat="server" ScrollBars="Both" Width="600" Height="300" Style="position:relative">
Please, keep the correspondence in a single thread so we can easily keep track of the message history. Thank you.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.