A multipage DjVu file had a bookmark for every page (14 pages thus 14
bookmarks in my test). I deleted pages 2 to 14 this way:

  $ for i in {14..2}; do djvm -d file.djvu "$i"; done

It removed the pages but neglected to touch the bookmarks. So when
viewing the document in evince it appeared at first as if no pages
were removed because the bookmarks sidebar still showed 14 bookmarks
to pages 1—14.

It was confusing, but I eventually realised that all but the first
page was in fact deleted as expected. The bookmarks were just dead
links. Clicking on a bookmark to a non-existent page does nothing. It
continues to show the first page as if that is the linked page and
gives no error.

What should happen:

Bookmarks to non-existent pages should probably be removed
automatically. Although we might imagine some obscure scenarios where
someone would want to delete a page and insert a replacement page
while maintaining the bookmark. But that would be a rare case. The
default action should be to remove bookmarks to non-existent pages
while it might be useful to have a