Reverting a customer back to 'Include in Dunnings' changes letter set to STANDARD

Hello,

We are using R12.2.9 and are currently implementing Collections into the business.

During testing we have found the following issue and I want to understand if it is intended functionality or not.

Scenario:

In Collections, query a customer account.

Menu bar, Actions, 'Exclude from Dunning'

Delinquent customer is not included in Dunning

Return back to customer account and 'Include in Dunning'

Run Dunning Plan and delinquent customer transaction is not flagged in report/letters

Looking at the customer account (site level), the Dunning Letter Set has been changed to 'Standard' and not the Dunning Letter Set which was originally set up.