Go to Monitoring > Events and choose a trigger in filter. Perferably not a popular one. Perhaps with only one generated event.
It then says "No events defined." Set period to "All", it still shows that no events defined. Now manually in URL make "period" larger. For example &perdiod=253823, add zero like so &perdiod=2538230 and reload the page.
Also notice that in filter "All" highlights in bold only now and not when clicked directly. When clicking again "All" event will dissapear from list.
See attached image.