[SalesForce] Can a partner community user login to an existing force.com site with customer portal

Although i have already verified that this is not possible in my current setup, it seems that salesforce (not support) are saying that we can.

So unless i am doing something really wrong here, i would think that nobody would be able to use a partner community license user and succesfully log into an existing force.com site that uses a customer portal for registration and login.

here are the steps i took to test this:

• deactivate an existing customer portal user
• enable the contact’s account as a Partner account before re-enabling the contact. (Communities must be enabled before this and a pool of partner community licenses must be available)
• When trying to reactivate the user record with a partner community profile, an error appears saying the username is already in use but there are no other users with the same username
• After changing the username to something else, we need to choose another community Nickname for the user because the previous one is in use although no other user has the same nickname
• I cannot add the new community profile to the existing customer portal that is used to register and sign in existing force.com site users
• Login attempts to the force.com site with the old and new usernames fail.
• Trying to reset the password on the force.com site for the old and new usernames fails because the usernames are not found. This is to be expected since i could not add the new community user profile to the portal in the first place.