This feedback item has been raised from this forum thread: http://www.telerik.com/community/forums/aspnet-ajax/combobox/enablecheckallitemscheckbox-all-entry-doesnt-fire-onitemchecked-event.aspx

This issue was first raised back in Sep '11 as it was suggested that 'it was in the plan for a future release'.

I've added this item here in the feedback portal to ensure that it's not got lost