When you delete an item (which has some trigger), then i see a successful green report: Item "Ping lost:icmppingloss[,3,1000,56,300]" deleted.
No details in the report about deleted trigger, and trigger already deleted !
Then history of events with this triggers is broken when you select to display All Group and Host. See attached picture.
It's not reproducible when you simply delete trigger, need to delete the item, which used in the trigger.