from:segment_1 statement in nav loop delivers wrong results

Question

While building a navigation like in https://www.youtube.com/watch?v=POgIsLeWGGQ I'm coming across a behaviour I don't understand.

My pages tree look like this:

I have the following code for the second level navigation:

{ nav:collection:pages :from="segment_1" }}
        {{ if ! no_results}}
            <li><a href="{{ url }}">{{ title }}</a></li>
        {{ /if }}
{{ /nav:collection:pages }}

the problem

When I'm on the homepage, the second level navigation shows me two entries, musicians and projects. As far as I understand, those two entries are in segment_1 so on home, no sub navigation should be shown.

What am I doing wrong?