Database Software

Could someone please help me understand what logic Oracle uses when one makes use of Oracles OLAP time dimension based on weeks.

I am use Oracle OLAP 11.2

I have a Time dimension that has the following hierarchy:-
YEAR
QUARTER
MONTH
WEEK

For calculating the weeks ID I make use ISO week and year i.e. IYYYIW
For calculating the end date I use the following:- NEXT_DAY( l_date, 'MON' ) -1
i.e. the weeks end date is the Sunday.
According to me this is the required result.

Problem is that for some months there are 3 weeks allocated which makes no sense to me.
I cannot understand the logic used in allocating the weeks.

The following is an example:-
the following weeks were allocated to the month February
201306 (end date= 10-2-2013)
201307 (end date= 17-2-2013)
201308 (end date= 24-2-2013)

but the following week was allocated to January which makes no sence to me,
I would have expected it to be found in February
201305 (end date= 3-2-2013)

Week 201309 (end date= 3-3-2013) was allocated to March which according to me is correct..

Another example is week *201030 (end date= 1-8-2010)* that is allocated to July while I would have expected that it should be August.

I would have thought that it uses the end date that is placed in the mapping to determine the month to place it in.
Could some one please explain what the reason for this could be.