When publication is configured using "User to Contact" mapper there are no X500 address stamped on the newly created stub Contacts. These X500 addresses are normally correspond to the LEDN of original users.
This behaviour is by design of "User to Contact" mapper.
Unlike regular stub users that have X500 addresses corresponding to the LEDN from the other organization, stub Contacts do not have them stamped. There is customized version of "User to Contact" mapper that has this functionality included. Please talk to your Quest Account Manager for further information on obtaining this.