Scheduled reminder for event sends email repeatedly

A scheduled reminder for an event where the reminder is set to fire "X days before the event start date".

The reminder should fire an e-mail on that date, should fire once, and then not fire again.

Instead, the reminder is sent every day starting on X days before the event start date, and every day thereafter.

(The cron job is set to run daily, I'm not sure if the reminder would go out more frequently if the cron job was set to run hourly.)

The repeat flag is not set for the scheduled reminder - see screen shot.