I am missing random months in the Calendar Grid View when either clicking to next month or going directly to "April" or "August". It seems to be months that don't have an event scheduled in them BUT I have tried to schedule an event to see if the month shows up and that doesn't work.
Here is an example:
Working correctly: http://westhills-montessori.com/calendar/
Missing April: http://westhills-montessori.com/calendar/2013-04/