Chapter number missing from most index entries

In a document which is numbered by chapter, the index entries reflect only the page number within a chapter. Entries appear as 2,5,5,7,2 instead of 3-2,1-5,4-5,2-7,3-2.

The root of this problem is discussed in Libreoffice bug 105628. The workaround is similar to that of a previous question ( Chapter number not in all TOC levels ). For indexes, the fix is

  1. Edit the index
  2. Add the Chapter Info field (also referred to as CI)
  3. While the CI field is selected, make the evaluate up to level a 1.