Are you saying:
Code:
<h3>So ein Ärger</h3>
becomes "So ein rger" in the toc?
Or are you saying that:
Code:
<h3>So ein Ärger</h3>
becomes "So ein rger" in the toc?
The first would surprise me, but the second example makes perfect sense. You can't have html entities ( Ä ) in the toc.ncx file.
You should either replace the html entities (that will be used in Sigil's toc generation) with their unicode equivalents or add a title attribute that uses the correct unicode character:
Code:
<h3 title="So ein Ärger">So ein Ärger</h3>
You should only have to do that with the header (h1, h2, h3... etc) tags that contain html entities and will be used by Sigil's ToC generation.
Or just fix the errors manually in the toc.ncx file after Sigil generates one.