Merging an external candidate with an Employee prior to Offer

Summary:

I have a customer scenario where an external candidate application on a requisition is identified as an Employee who should have applied via the Opportunity Marketplace rather than externally. In this scenario where the recruiter identifies this manually, I am not able to search for the Employee and perform a merge, i.e

1. Click the "Search for duplicates" link
2. Click the "Select other potential duplicates" link to open the search window:
   The list displayed on the duplicate drawer are external candidates. Are we NOT expecting to see employees here at all?

I understand that the automated 1st duplicate check prior to Offer does not take the employee into account and that the employee is only taken into account post offer.