When I try entering the End Date of a Campaign using the calendar icon, I am unable to select a date past the month of May. Trying to do so makes the calendar go blank and I then have to type in the end date manually.
The calendar is Joomla core library code, so It should work . Maybe there is javascript confict on your site . Could you please submit your site information via support ticket system so that I can check and fix it for you ?