Deleting Records in Related Tables

Hello All! I need your help. I have created a database with one "main" table and several other "sub" tables that are linked back to the "main" table via a common field in the relationships screen. My layouts are setup to have the database open in the "main" table's layout and then switch to other layouts that are defined in one of the "sub" tables environment based on which table I'm using. Any other information I need in one of those layouts from another table I generally view via a portal.

My problem is this: While in one of the "sub" table layouts, I will perform a find which works beautifully. However if I want to delete the found set, it will end up deleting not only the found records, but ALL records in that particular table with the same value in the common field (primary key if you will) that is used to link the records back to the "main" table. However, it does NOT delete the related common field record in the "main" table. I have tried to edit the relationship options, but nothing seems to work. I have tried to just delete one record instead of a found set, but the same thing happens.

Any ideas?:

Shane