prerequisite :

• a taskchain activity is created
• some attempts are recorded

steps to reproduce :

• in the navigation menu, expand the 'Class reports' node of the taskchain activity
• click on the 'Chain grades' link
• check some checkboxes of the 'Select' column
• click on 'Delete attempts'
• confirm the deletion

what you should get :

• the selected attempts should not be listed anymore

what you really get :

• the selected attempts are still there