Case Activities no longer show overdue items first.
Previously, the listings of activities on cases would show overdue items first.
When datatables were being integrated CRM-16363 https://github.com/civicrm/civicrm-core/commit/ad280fb669e26f136bb9f56b29556ad70a78d3a6#diff-ff123c4a302e96ad0dfa6e93247dd242 they added a sort order to the table directly int the template file - resulting in this:
The logic to sort by overdue items first lives in the Case/BAO/Case.php file (line 1042 in 5.5.3)
ORDER BY overdue_date ASC, display_date DESC, weight DESC";
Simply removing the data-order 'filter' from the tpl file reverts to the previous behavior. I've put in a PR as well.