This is mostly an simple error checking bug in es_sup_edit_position_schedule.php.
While creating a new schedule for a given position, if the end date for the schedule is left blank and the user tries to save the schedule, a large number of SQL errors (see attached text file) are displayed on the page.
If the start date is left blank, the schedule is saved with a start date of 01/04/1970.
Checking the input and displaying a message to the user would be useful.
the errors