Any idea why a SqlDataSource control might wipe out most of the data in the record after it does an update?

I have a GridView which has only 4 columns. The underlying table has like 100 columns, and the SqlDataSource, which I generated automatically using the QueryBuilder, has parameters and statements for all the columns. After the GridView processes an Update, using the default Edit and Update LinkButtons, only the 4 columns in the GridView remain populated (and indeed updated with the new data). The rest are wiped out and set to null.

What am I doing wrong here? Thanks in advance.

Aaron