Jack Chang said almost 7 years ago on FullCalendar Events and Scheduling :

NVM, I found the problem in  https://github.com/driftingruby/042-fullcalendar.

In app/views/events/create.js.erb and  app/views/events/update.js.erb

$('.calendar').fullCalendar(

 'renderEvent',

  $.parseJSON("<%=j render(@event, format: :json).html_safe %>"),

  true   //  <-----

);

the 'stick' atttibute for  'renderEvent'  method  should be set to false