Strange DataView behaviour

I am facing a strange behaviour of dataviews. In a comfort of routine, I added a oledataadapter to my form and connected to a table in the database-tb1-, generated a dataset-ds1- and then added a dataview-dv1- whose table properites is set to ds1.table.

The problem is when i use the following method to change the data in dataview, changes affect the dataset correctly but when the database is updated using the dataset some columns of some rows are not affected at all!!

the method i use is this:

dv1.item(rn)(clm)=x

where rn is the row number, clm is the clm index or clm name and x is the desired data.

To work around this problem i used the alternate way to change the data and that worked perfect. The other method is this

dv1.item(rn).row.item(clm)=x

I wonder if the first method is not a proper method, why only SOME ROWS and SOME COLUMNS are not updated despite the dataset holding the correct data?