random values in semi-aggregate measure in crosstab report

[kiran.timsina]

I have two tables as:
1. On Hand- item/location/day/OH qty
2. Time Day- day/week_number/month_name/year

Join:
inner join on day

Dimensions defined:
Regular dimension- Year, Month_Name (I had to make them separate reg. dim. because the same month can fall under two years)
Measure dimension- OnHand (aggregate rule of oh_qty is defined to "last" for both "Year" and "Month_Name" reg. dim.)

Now, I try to make crosstab report year versus month. What I get is random weekly ending on hand(EOH) values. Sometimes I get EOH of week 1 as the EOH of that month and sometimes I do get EOH of week 4 as EOH of that month.
This( http://pic.dhe.ibm.com/infocenter/cbi/v10r1m0/index.jsp?topic=%2Fcom.ibm.swg.im.cognos.ug_fm.10.1.0.doc%2Fug_fm_id8708usage_aggregation_properties.html) link says nothing more.

Any clue of what I am missing. Help me cognoise guys, as always!  :)

Edit: "first" aggregate rule is working though to get beginning on hand.