Hot key in Button XAML

I have this code;

 <StackPanel>
         <WrapPanel>
             <Label Content="_Texto" Target="{Binding ElementName=TextBox1}" />
             <TextBox Name="TextBox1" TextWrapping="Wrap" TabIndex="0" Margin="2" Width="230" ></TextBox>
         </WrapPanel>
         <Button Content="_Boton" Height="23" Name="button1" Width="75" TabIndex="1" IsDefault="True" />
</StackPanel>

Even if the default focus on the button does not seem to work, I press Enter or space and it never activates ... I've also noticed that the Enter never works, not the space, if I do a click with the mouse on the button, immediately, if you execute the keystrokes from the keyboard (but only paying attention to the space bar ...) Do you have to take into account any configuration?