The use of eo_check_datetime() on line 375 of event-organiser-edit.php (source) doesn't specify a time. Consequently any added date is assumed to have the current time, instead of the event's time.

This was originally reported here: http://wordpress.org/support/topic/changed-recurring-event-has-the-wrong-time?replies=2