XAML: why is button on top when I clearly said to go on bottom?

Answer 1

The StackPanel is meant to take it's sizing from it's elements and it's container (depending on it's orientation), although what you've done looks correct, that's not the way the StackPanel is "meant" to be used. Although it looks like it's the height it's set, it's actual height (that it uses for laying out child controls) is the size of it's content (the button). The StackPanel has it's uses, but if you are doing anything other than a simple stack of controls then you generally should be using something else.

You can fix it by either sticking a sized grid inside:

<StackPanel Width="300" Height="50" Background="Red">
          <Grid Height="50">
            <Button Name="Switch" Content="Switch Page" Width="100" Height="20"
            HorizontalAlignment="Right" VerticalAlignment="Bottom"
            />
          </Grid>
        </StackPanel>

Or, for that particular layout, you might want to look at DockPanel, which will behave more like you would expect it to.