ComboBox.SelectedIndexChanged cause page postback when using multiView And updatePanel.

Hi

i have a multiView with 5 views which placed inside updatePanel like this :

<asp:UpdatePanel ID="UpdatePanel4" runat="server"><ContentTemplate><asp:MultiView ID="MultiView1" runat="server" ActiveViewIndex="0"><asp:View ID="View1" runat="server"></asp:View><asp:View ID="View2" runat="server"></asp:View><asp:View ID="View3" runat="server"></asp:View><asp:View ID="View4" runat="server"></asp:View><asp:View ID="View5" runat="server"></asp:View></asp:MultiView></ContentTemplate></asp:UpdatePanel>

my problem is that, i have some comboBoxes inside my views, when i change selectedIndex, it cause the page to be postBack and i think the updatePanel does not works correctly!!!

can anybody plz provide some information which how to prevent postBack when comboBox_selectedIndexChanged event occure.

thanka in advance