The moderators' Community Events page (
/admin/community-events) makes it too easy to put in an invalid entry for creating an event and not notice.
The form for creating events does provide immediate validation of entries, so, for example, if you put in a too-short title, the entry box turns red, and it gets a caption indicating how many more characters you need to enter.
However, the "Create Event" button at the bottom remains enabled even if the entries aren't valid, and if you click it, you are returned to the list of events at the top of the page. At that point, if you don't check the list for your new event or scroll down to see the still-filled entry form with an error message at the very bottom, you'll think that your event has been added.
The simple fix (hat-tip to Monica Cellio) would be to disable the Create Event button until all required fields have valid contents. That way, you'll never think that you've created an event when you haven't.