When editing an event, it can be confusing to the user that certain dates cannot be selected if they try to edit the end date first. It would be more intuitive to allow them to select any date while editing, but prevent the event from 'Saving' if the dates don't make logical sense.
Or to at least have a pop up with instructions on how to do the updating properly. We just had an admin who couldn't figure out how to change the date of a vol event. Turns out we had to chance the end date first and then could change the start date. That is not intuitive.