BUG RC12 : html ToC in epub3

When In create a html-toC in epub 3 and I name it, the epub shows the titel twice.
When I don’t give it a title, I get a German word - and only one, as it should be - instead of the language the book is written in
.[attachment=0]Screenshot 2020-12-03 103948.png[/attachment]

That doesn’t happen in epub2. There the ToC comes out just fine.

Sorry, but I could not reproduce this. Have in mind that this could also depend on the viewer application you are using. Please, upload a small project with few documents that shows the problem and I will have another look at it.

This is how my ToC looks like with some example documents:
[attachment=0]Screenshot 2020-12-04 11.37.50.png[/attachment]

I used calibrre to check it.

I tried it againwith this new project and it’s the same.