I'm using the 'Break comments into pages' option under 'Discussion' and have set it as follows:
Enable threaded (nested) comments 2 levels deep
Break comments into pages with 50 comments per page and the first page displayed by default
Comments should be displayed with the older comments at the top of each page
The comments now display almost exactly as desired. However instead of grouping 50 comments per page it unevenly: for example one thread has 87 on the first page, then 61 on the next with no obvious pattern. What's gone wrong?