Wrong results for _week_of_year

[hsu29]

Using _week_of_year(<datetime field>) within a report returns some wrong data:

Date                  _week_of_year resullt
2007-Jan-01      52  (wrong)
2007-Jan-02      52  (wrong)
2007-Jan-03      1    (OK)
:
2007-Jan-08      1    (wrong)
2007-Jan-10      2    (OK)

It's seems it sets the week beginning on Wednesday for this report... don't know why?

The most confussing is that after creating a completely new (blank) report that only includes a column with the expression

         _week_of_year (2007-01-01)

it returns = 1, which is OK!

Does anyone have any clue about what's happening?
I don't know what to do

Thanks a lot

[tiga123]

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