The pattern used to parse the date is dd,MM,yyyy
, which means day followed by a comma, followed by month, followed by a comma, followed by year.
You enter 08/18/2013
. 08 is a valid day, but 18 isn't a valid month. And you should enter commas, not slashes.
Since you enter 18/2013 as the month, it's interpreted as the 18th month of 2013, which corresponds to the 6th month of 2014 (since years, well, have only 12 months): June.