What is the "Attach (object)" for?

It seems to me that "Attach (object)" is used for changing where a specific record is related. But there is something not right. Could you please tell me the correct behavior given the scenario below? 1. Go to Generic PERA Application -> Contributors. Select a particular Contributor. Under this contributor, you will see "Number of PERA" which is a counter of "active" PERA records for this Contributor (meaning Account Closed Date is null). 2. Under PERA related list, click Attach PERA. 3. From the list that comes out, select a PERA record from a different contributor. You will see that this record is automatically added in the Contributor's PERA list. 4. Just to be sure, refresh the Contributor's view page. You will see that the number of PERA for the Contributor has not changed. 5. Same t