thanks for your reply. The double-footer was a mistake while copying the code into the forum. It's correct in the original code.
But I played around with it a bit more and found the problem. I had to specify a data-title attribute or the layout would not render the header at all, which contains:
If I remove the span with the view-title role, it works fine without data-title.
Strangely enough, this happens only for additional layouts, not for the first one defined as "default". It renders fine even with the constellation above. That's why I didn't realize the problem at first.