Unexpected update to Access DB when using a Strongly Typed Dataset

I am working with a Strongly Typed Dataset which I Fill from an Access2000
DB. I am using VS2005 and VB.Net. Perhaps I am missing something, but the
observed problem is:
Given a sub-set of Rows from a Table in that Dataset, code in the following
form behaves unexpectedly:
For Each DR as DefaultDataSet.BasicInfoRow in subset
DR.Field1 = NewValue
Next

The unexpected result is that with a breakpoint set on the Next statement, I
can observe the Field1 values changing IN THE ACCESS DB. Note the absence of
any explicit Update statement. In fact I discovered this when my subsequent
Update threw an:
DBConcurrencyException: Concurrency violation: the UpdateCommand affected 0
of the expected 1 records
Interestingly enough, the For loop was changing 10 - 20 Rows, all of which
are properly updated in the Access DB and they were updated at the time the
DataTable Row was updated.

For other reasons, I do have a Handler for the BasicInfoRowChanged event,
which is raised for each change. I do not do an Update in that Handler. Nor
do I see an Update in the generated DefaultDataSet.Designer code which I step
thru.

My understanding is that making a change to the DataTable is a
DataTable-only operation and should have no effect on the original DB. I
expected that changes to the DB would ONLY occur when explicitly requested
via a DataAdapter.Update(...) statement. What am I missing here? I have not
tried this outside of the VS2005 environment (ie a Release version run
standalone).

--
Jim Parsells