2221708 - CALWEEKOFYEAR() gives different results in SAP IQ and SQL Anywhere

In IQ, date function returns unexpected values.

Example. Week number CALWEEKOFYEAR (Abbreviation cwk) for date '2014/12/29'.

In IQ :

select datepart(cwk,'2014/12/29') from iq_dummy ;
datepart(cwk,'2014/12/29')
--------------------------
                        53

 That '2014/12/29' is day of last week of year 2014.

In SQL Anywhere :

 select datepart(cwk,'2014/12/29')
datepart(cwk,'2014/12/29')
--------------------------
                         1

The date '2014/12/29' is a day of First week of 2015.

How this difference can be explained?

SAP IQ 15.4

KBA , BC-SYB-IQ , Sybase IQ , How To