Here's a newbie question

I have a SQL server portfolio database with 3 tables - holding, owner, safekeeper.
The holding table keeps the postion data and the other two are reference tables

I created LING to SQL classes from the DB, created a datasource from the obects.

I created screens to add, delted and change owners and safekeepers by dragging the objects from the data source, added a couple of lines of code, and they're rocking and rolling.

Now I'd doing the holding form. I dragged all the fields over from the object and all is well with one exception:

When I change the ownerID field in the holding table, the text box appears to changes but the save ignores the changes.
Before the change, the textbox displays the correct value, but it won't take the change.
Other fields, such as face value, maturity date, etc, save as they should, but not the ownerID. The databinding doesn't seem to be working, but I checked and it's there and pointing at the ownerID field.

I put relationship in the DB to indicate that ownerID is a foreign key relating to the owner table, and I can see that the datasouce has done something with those relationships- but I can't find any reference to tell me what to do with them., if anything, or how they affect databinding.

Any clues?