page number by chapter has incorrect index entries

The document discusses subnet mask three times, around page 2-2, page 2-8 and 4-7. In each case, the term “subnet mask” is marked to be included in the index. I wanted an index entry something like:
subnet mask: 2-2, 2-8, 4-7. Combine identical terms is checked, otherwise I’d get three lines in the index (subnet mask 2-2, subnet mask 2-8 and subnet mask 4-7). What I get is

subnet mask: 4-2, 7, 8

This is incorrect. A similar bug number 60616 (https://bugs.documentfoundation.org/show_bug.cgi?id=60616) was opened sometime back.

Yes, that is a bug, and its status is “NEW” (unfortunately, not fixed). So, what is your question?