Thank you much for the detail! I can reproduce this now. It looks like the event itself isn’t really being duplicated, so much as a bug in the monthly view is causing events in the last half-hour of the day to bleed onto the next day as another calendar entry. It doesn’t appear to impact the Year/Week/Day views in my test.
Glad it isn’t impacting the actual functioning of your scheduled event (at least anymore). I’ll get this logged for a fix in a future update to the product.