Editing a comment drops its status update information

Issue Summary

If you add a comment to change a case's status etc. the update information is saved and displayed (e.g. 'Priority: 2 >> 3' etc.) However if you subsequently edit the comment, the original status is forgotten. So for example if you add a comment to change priority from 2 to 3 and then subsequently edit the comment and change the priority to 4, the change is shown as '3 >> 4' rather than '2 >> 4'. This is especially confusing if you edit a comment without making any status changes (changing only the text of the comment for example) - as now the previous status change is not displayed at all.