Created attachment 98649 [details]
This is a copy of my actual bank spreadsheet from which personal data has been replaced with dummy data and example data.

When the FORMAT CELLS is set to DATE and the date is entered as year (dot) month (dot) day (e.g. 2014.05.08), the spreadsheet is saved and closed then reopened again either same day or some number of days later, the date is decremented by two days (e.g. 2014.05.06).  The bug manifests by decrementing the date by two days each time an entry is made or modified, and does not matter whether the year month date are separated by a dot (.) slash (/) or hyphen (-).

Under the FORMAT CELLS options, I have the date Format Code set as YYYY"年"MM"月"DD"日" so that it shows me the year followed by the Japanese character for year, then the month followed by the character for month, and date followed by character for date.

When I type "locale" in a terminal, the result returned is: 
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=ja_JP.UTF-8
LC_TIME=ja_JP.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=ja_JP.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=ja_JP.UTF-8
LC_NAME=ja_JP.UTF-8
LC_ADDRESS=ja_JP.UTF-8
LC_TELEPHONE=ja_JP.UTF-8
LC_MEASUREMENT=ja_JP.UTF-8
LC_IDENTIFICATION=ja_JP.UTF-8
LC_ALL=