Depending on the locale of the server's operating system, the WEEK function used on a Sunday may return the next week, as Sunday is set as the first day of the week.

This can be tested with

SELECT WEEK('2014-01-05')

which will return 1 on a German locale and 2 on a US locale.

In order to set Data Virtuality Server to the German locale, append the following line to standalone.conf.props.bat (Windows):

set "JAVA_OPTS=%JAVA_OPTS% -Duser.country=DE -Duser.language=de"

On UNIX systems, append the following line to standalone.conf.props:

JAVA_OPTS="$JAVA_OPTS -Duser.country=DE -Duser.language=de"