Control inside repeater causing full postback even after keeping in update panel - asp.net

Question

In my page, I have one search button and a repeater. I have wrapped everything inside UpdatePanel. My search button do not causes full postback, i.e ideal but RadioButtonList inside Repeater control does. I have no idea what to do.
<asp:UpdatePanel ID="up" runat="server">
<ContentTemplate>
<table align="center" border="1" cellspacing="0" class="tabmn6">
<tr id="trheader" runat="server">
<th id="trEdit" runat="server">Edit</th>
<th>User Name </th>
<th>Role</th>
<th>From Date</th>
<th>To Date</th>
<th>Comment</th>
<th>Status</th>
</tr>
<asp:Repeater ID="rpUserDetails" runat="server" OnItemDataBound="rpUserDetails_ItemDataBound">
<ItemTemplate>
<tr>
<td id="tdRPEdit" runat="server" align="center">
<input type="button" class="editbtn" name="btnEdit" id="btnEdit" runat="server" onclick='<%# string.Format("javascript:return AddBoardCast(\"{0},{1}\")", Eval("BC_ID"),"Edit") %>'>
</td>
<td id="trRPTL" runat="server" align="center">
<asp:Label ID="lblUName" runat="server" ForeColor="Red" Text='<%#Eval("UserName")%>' />
</td>
<td align="center">
<asp:Label ID="lblRoleName" runat="server" ForeColor="Black" Text='<%#Eval("RoleName")%>' />
</td>
<td align="center">
<asp:Label ID="lblToDate" runat="server" ForeColor="Black"><%#DataBinder.Eval(Container.DataItem, "BC_FromDate", "{0:dd/MM/yyyy}")%></asp:Label>
</td>
<td align="center"><asp:Label ID="lblFromDate" runat="server" ForeColor="Black"><%#DataBinder.Eval(Container.DataItem, "BC_TODate", "{0:dd/MM/yyyy}")%></asp:Label></td>
<td align="center" width="20%">
<div style="color: black"><%#Eval("BC_Comment")%></div>
</td>
<td align="center">
<asp:HiddenField ID="hdnBC_ID" runat="server" Value='<%#Eval("BC_ID") %>' />
<asp:HiddenField ID="hdnUserID" runat="server" Value='<%#Eval("UserID") %>' />
<asp:RadioButtonList ID="rdStatus" runat="server" Height="48px" RepeatDirection="Horizontal" AutoPostBack="true" OnSelectedIndexChanged="rdStatus_SelectedIndexChanged" CssClass="rad">
<asp:ListItem Text="Active" Value="1"></asp:ListItem>
<asp:ListItem Text="Deactive" Value="0"></asp:ListItem>
</asp:RadioButtonList>
</td>
</tr>
</ItemTemplate>
</asp:Repeater>
</table>
</ContentTemplate>
</asp:UpdatePanel>