Mysql query cache?

Hello.
I have a strange problem with my website at work. There is a database
with some product data. Data is registered thru php - website, and
once a week a raport is generated from this data. If a mistake was
made, the data of current week can be corrected in the same way as it
is input. Also there is a part which draws graphs showing registered
data on time based graph.
The problem is, since 2 days something happened and the report
generated shows invalid data - from the current week, not the most
recently corrected. I don't keep corrected data. It's no longer in
database. But it appears in the report. In the graph showing part the
problem doesn't exists. The most recent data is shown there. And
still it uses the same data table.
The problem never happened before (the website exists for many
months).

I'm looking for some advice what could have happened? After rebooting
the computer-server the most recent data was loaded into the report,
and the problem continued if any new corrections were made after the
reboot.

It looks to me that it is some kind of a buffer which holds the
queries...?

I even have screen-printed the query and - following - the results. If
I executed the screen-printed version in SQL-yog - a SQL managing
program - the result was correct. But still in the application - the
data was not up-to-date.

The screen -printed query is:
"select
columns_wr.nazwa2,weekly_sales.value,weekly_sales.week,weekly_sales.week,columns_wr.event2,columns_wr.product_id
from report.columns_wr,report.weekly_sales
where columns_wr.product_id=weekly_sales.product_id
and columns_wr.product_id=65
and date>='2007-12-10' and date<='2008-01-13' order by date"