Yes Paul, it occured to me that it was based on a query but you did say it was based on a table.
So check your recordset, open it as a query dataset, if the navigation button below hides the new record, then your query is not updateable.
you can take out the appended table and just create a lookup field in your main table. Check the northwind database , form "Products".
It is based on one table, yet the Control - Category, get its row source data from a query.
Check the properties of the control- Category Id, see how it gets its data.