I created an two-column index for a document that looked great as shown in first image below. When I went back to the document and updated the index, the format changed and was really ugly, shown in second image below (with formatting marks). I have not been able to recreate it with any version of LIbreOffice, on Windows, or on a Mac.
I deleted the most of the content of the large document and replaced it with some content pasted from elsewhere with index entries inserted. I updated the index and it looks not bad, but is using the same index settings as the one that did not look good (as shown below). I am attaching that two page document.
(encoding adjusted by ajlittoz to allow access to attached file)