The following is a simple page setting up with two forms. While I click "Submit 1", client side error occurs. Anyone can help?

 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>Form Error</title>
</head>
<body>
    <form runat="server" id="theForm">
        <ext:ResourceManager runat="server" ID="theManager" IDMode="Ignore" Theme="Access" EnableViewState="false" ManageEventsViewState="false" />
        <ext:Viewport runat="server" Layout="fit">
            <Items>
                <ext:Panel runat="server" Border="false">
                    <TopBar>
                        <ext:Toolbar runat="server">
                            <Items>
                                <ext:Button runat="server" Text="Submit1">
                                    <DirectEvents>
                                        <Click CleanRequest="true" FormID="Form1" Method="POST" 
                                            Url="/Organization.aspx/_ToSave" />
                                    </DirectEvents>
                                </ext:Button>
                                <ext:Button runat="server" Text="Submit2">
                                    <DirectEvents>
                                        <Click CleanRequest="true" FormID="Form2" Method="POST"
                                            Url="/Organization.aspx/_ToSave" />
                                    </DirectEvents>
                                </ext:Button>
                            </Items>
                        </ext:Toolbar>
                    </TopBar>
                    <Items>
                        <ext:BorderLayout runat="server">
                            <West>
                                <ext:FormPanel runat="server" ID="F1" FormID="Form1" Title="Form1" Width="300">
                                    <Items>
                                        <ext:FormLayout runat="server" IDMode="Static">
                                            <Anchors>
                                                <ext:Anchor Horizontal="100%">
                                                    <ext:TextField runat="server" ID="West_Field1">
                                                        
                                                    </ext:TextField>
                                                </ext:Anchor>
                                            </Anchors>
                                        </ext:FormLayout>
                                    </Items>
                                </ext:FormPanel>
                            </West>
                            <Center>
                                <ext:FormPanel runat="server" ID="F2" FormID="Form2" Title="Form2">
                                    <Items>
                                        <ext:FormLayout runat="server" IDMode="Static">
                                            <Anchors>
                                                <ext:Anchor Horizontal="100%">
                                                    <ext:TextField runat="server" ID="Center_Field1">
                                                    
                                                    </ext:TextField>
                                                </ext:Anchor>
                                            </Anchors>
                                        </ext:FormLayout>
                                    </Items>
                                </ext:FormPanel>
                            </Center>
                        </ext:BorderLayout>
                    </Items>
                </ext:Panel>
            </Items>
        </ext:Viewport>
    </form>
</body>
</html>
Error Screen shows like the following

Click image for larger version. 

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Saying length is undefined.

I've tried to erase FormID attribute in DirectEvents.Click, works fine but those fields belong to Form2 and ViewState were submitted and that's not I really wanted (or, do I need to live with it?).