No way to distinguish the core and custom fields on Find and Merge Duplicate Contacts page

There is no way to distinguish the core and custom fields on Find and Merge Duplicate Contacts page. This is particularly confusing as one of the clients had a custom field named email and created the rule using this custom field and every time someone registered an event which was configured with this aforesaid rule it was attributed to a new contact.

We should be using Custom Field: Custom Group format to avoid confusion as we do elsewhere in Import mapping screens, etc.