Summary:

Some menus contain records that have sub-records.  For example, division records in the Divisions menu, have class records that are attached to each division record.  These class records are termed "sub-records".  Other examples are Fees for Exhibitor records, Buyer transactions for Sale records, and so fourth.

Clicking on the "Delete" button on a parent record will not only delete the parent record but all sub-records that are attached to it.  This is by design.

In order to delete one or more sub-records of a parent record, place your cursor in a field of a record (or sub-record) that you want to delete and click the "Delete" button.