Manage-Database- Relationship tab
Check your relationships and see if the "Delete related records in this table ..." box is checked for any cases where it would cause that to happen.
OK, removing ALL the "delete when..." checkboxes fixed the problem.
But WHY? Seems if I delete a record in the main table view, that it is reasonable to delete the record in the portal view. So, why does it delete everything?
That would depend on what options you specified in the relationship. Correctly set up, the "delete" option will do exactly that. Set up incorrectly, and you get a "cascading delete" that can delete far more records than you want.
Say you have this one to many relationship:
where the two table occurrences refer to different data source tables. This should not be a self join for this example.
If you double click the line between the two occurrences and select the delete option only for the Portal table, then deleting a record in LayoutTable will also delete all and only the related records in Portal Table.
But a delete option affects what happens when a record in LayoutTable is delete no matter what layout you are on and no matter what table occurrence of LayoutTable is specified for that layout.