The minus button for deleting kern pairs in the kern palette is bugged. When deleting a kern pair that contains a kern group (A, @T) it will often delete the last kern pair in the list instead of deleting the selected kern pair. This happens almost every time if the selected pair was selected automatically after deleting a different pair. It only happens about half the time if the selected pair was selected manually.
Edit: this is Version 2.2.2 (826)