Radgrid update button is not working when RadCombobox inside this grid having AutoPostBack property true in IE11

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ASP.NET

C#5.0

I have radCombobox in RadGrid. While adding new records through RadGrid. When select any record from
combobox, I m filling description regarding it into next textbox of that grid through SelectedIndex event of Combobox and then when click on insert button of grid. It is not proceeding anything. How to resolve this issue??
It's not working only in IE10 and IE11 browsers, in fact working fine in other browsers.
Its also working fine whenever auto postback property set false of that combobox for all browsers. But this case not useful as have to use SelectedIndex.