ModComment Roll Up not retrieving Comments from all related Contacts in Opportunity

In an Opportunity there are two ways a Contact can be related to it.

1. A single Contact is related by the Contact Name reference field
2. Multiple Contacts can also be related under the Contacts "tab" of the Opportunity using a many-to-many related list where the relationship is stored in (I think) vtiger_contpotentialrel

Any Contacts related to an Opportunity in 2. are not being retrieved in the getCommentEnabledRelatedEntityIds() method of the parent's Record Model.