When you add a button to a form which causes validation, the validation is not evaluated on the client side, just the server.
<ExtJS:ScriptManager runat="server" StateProvider="PostBack" Theme="Gray" />
<form runat="server">
<asp:ValidationSummary ID="vsSummary" runat="server" HeaderText="The following requires your attention:" ShowMessageBox="True" ShowSummary="False" />
Name: <asp:TextBox ID="txtName" runat="server" Width="255" />
<asp:RequiredFieldValidator ID="rfvName" runat="server" ControlToValidate="txtName" ErrorMessage="Name is a required field!" Display="Dynamic">!</asp:RequiredFieldValidator>
<ExtJS:Button ID="btnSubmit" runat="server" CausesValidation="True" Text="Submit" />
<asp:Button ID="btnSubmit2" runat="server" CausesValidation="True" Text="Submit 2" />
</form>
The above demonstrates that the ExtJS button does not issue the validation on client side, only on server side 
Cheers,
Timothy
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Timothy Grant Vogelsang
tvogelsang [at] gmail [dot] com
Coolite Toolkit 0.7 SVN (Professional Edition)
Microsoft .NET Framework 2.0
Microsoft ASP.NET Ajax 1.0