Unable to schedule recurring calendar events with an end date.

When adding recurring calendar events the system indicates an incorrect date format, even though the date was selected via the calendar widget and the format appears to be correct. The issue does not happen when creating single-day events.
Troubleshooting seems to indicate that the issue is associated with setting an end date. If I don't set an end date then the recurring event is added to my calendar. I tried to use that as a work-around by then editing the recurring event to add an end date, but the end date option is apparently disabled during edit (though I don't know why that would be).

See screenshot.

This appears to be a recent bug, as I have been able to create recurring calendar events with end dates only a week or so back.