I am trying to set TabStrip's AutoGrow to true, but in my opinion it's not working as expected

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<!DOCTYPE html>
<html>
<head runat="server">
</head>
<body>
    <form runat="server">
        <ext:ResourceManager ScriptMode="Debug" Theme="Crisp" runat="server" />
        <ext:Window runat="server" Title="Standard" Closable="false" Layout="FitLayout" Height="250" Width="500" AutoScroll="true">
            <Items>
                <ext:Panel Title="Tab Panel" runat="server">
                    <TopBar>
                        <ext:Toolbar runat="server">
                            <Items>
                                <ext:TabStrip AutoGrow="true" runat="server">
                                    <Items>
                                        <ext:Tab ActionItemID="_pnlExtNET" Text="Ext.NET - Ext.NET" />
                                        <ext:Tab ActionItemID="_pnlSencha" Text="Sencha - Sencha - Sencha" />
                                    </Items>
                                </ext:TabStrip>
                            </Items>
                        </ext:Toolbar>
                    </TopBar>
                    <Items>
                        <ext:Panel ID="_pnlExtNET" Title="Ext.NET" Html="Ext.NET" runat="server" />
                        <ext:Panel ID="_pnlSencha" Title="Sencha" Html="Sencha" runat="server" />
                    </Items>
                </ext:Panel>
            </Items>
        </ext:Window>
    </form>
</body>
</html>
I wonder how to configure TabStrip to auto grow / shrink.

Thanks in advance.