2 Answers

In all lunar calendars the first day of each month depends on the phases of the moon. Some calendars begin their month at the start of the new or dark moon while others do not start the month until the first new crescent moon is observed. 

The actual time it takes for the moon to go through a complete phase cannot be perfectly subdivided by any full number of days. It takes a little more than 29.5 days for this phase to occur, and, thus, over time, lunar calendars will begin to slip and become more and more inaccurate over time. http://wiki.answers.com/Q/Why_would_a_lunar_calendar_be_inaccurate?#slide=1

300AD we went to the solar callendar. The lunar calendar was proven to be less accurate and our present system is flawed as well more than just the leap year correction.