Hi h_classen -
I see how this is working well in your published output. But when I attempt to preview or publish, on my side the menu element disappears. It's sticking to 0px within the container. It's still there it's just up under the scroll.
I've been scratching my head trying to figure out why my published output behaves differently than yours. I see what yours is doing and it looks like it should work in mine but it's not:)
This is the same issue I ran into last week. I ended up creating a separate DIV for my menu. Works great but I'd love to figure out why yours isn't working for me.