Setting DefaultButton on a page with MultiView control does not work with Enter key

Hello everybody, I have an ASP.NET Web Forms application targeting the .NET Framework 4.
In this application I have a page where submitting a form by pressing the Enter key does not work. In the specific, when I press the Enter key the page refreshes without submitting the Form. This Button is inside a View of an ASP.NET MultiView control, the Form, form1, is declared in the Master Page and therefore embraces the MultiView
In order to specify the button to be "clicked" when I press the Enter key, taking into account that it is embedded in a Master page, I placed the following code in the Page.LoadComplete event handler:
(aspx) <asp:MultiView ID="mvDownloads" runat="server" ActiveViewIndex="0"> <asp:View ID="viewSearch" runat="server"> <asp:Button ID="btnSubmit" runat="server" UseSubmitBehavior="true" Text=& ...