Alright, I figured this out on my own. In my version of wp-admin/edit-comments.php The following line is inserted:
list($_comments, $total) = _wp_get_comment_list( $comment_status, $search_dirty, $start, $comments_per_page ); // Grab a few extra
Since the variable $comments_per_page is set to default at 20, this means that 25 comments are grabbed. The extra 5 comments are sliced off into an array called $extra_comments which are then outputted on the page, but hidden from view. So if you click every comment this isn’t a problem since those extra comments are never used, but when mass edit happens they are checked inadvertently.
It looks like this was already fixed just a day ago. But posting so other people can learn about this.
https://trac.www.ads-software.com/ticket/7433
