Instead of using MouseLeftButtonDown or MouseLeftButtonUp, you should use the Click event to detect a button click by the user. Because of the way that the ButtonBase class handles mouse events, MouseLeftButtonDown and MouseLeftButtonUp events do not occur when the click mode is a value other than Hover.

The following example demonstrates handling the Click event of a Button and setting its IsEnabled property.

Private Sub disableButtonClick(ByVal sender As Object, ByVal e As RoutedEventArgs)
    disableButton.IsEnabled = False
End Sub

void disableButtonClick(object sender, RoutedEventArgs e)
{
    disableButton.IsEnabled = false;
}

        <Button x:Name="disableButton" Width="200"
        Click="disableButtonClick" Content="Disabled when clicked" />

Silverlight

Silverlight for Windows Phone

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Reference