For the time being you can either skip the selects elements from decoration:

ASPX:

        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" ControlsToSkip="Select" />
        <div id="div1">
            <telerik:ReportViewer ID="ReportViewer1" runat="server" Height="492px" Width="927px"></telerik:ReportViewer>
        </div>


Or decorate only particular zone that do not include the ReportViewer:

ASPX:
        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" DecorationZoneID="div2" />
        <div id="div1">
            <telerik:ReportViewer ID="ReportViewer1" runat="server" Height="492px" Width="927px"></telerik:ReportViewer>
        </div>
        <div id="div2">
            <input type="text" name="name" value=" " />
            <select>
                <option>option1</option>
                <option>option2</option>
                <option>option3</option>
            </select>
        </div>