Why does advancing/retreating the month remove all events from the calendar in FullCalendar?
Looking at your calendar now it looks like you have it fixed.  I was gonna' offer the solution that I was told:  Make your site's short date format to use "2014-5-19 17:30"  Unfortunately it had to be in military time, not 12 hour or it didn't work.  That is only an issue when looking at the "upcoming events" that I have listed at the bottom of my calendar in another block.  I was going to go the ajax method if I can get 12 hour time to work with ajax, using the fix offered for Ajax at the drupal posts on this issue; haven't tried it yet.  

So what solution did you get to work for you?

Dave N