[xim]

Steve, we do not see the reason to have admin and customer accounts for the same email and work with these accounts as separated.

Moreover, using the information that admin is surfed through customer area we can show special feature for him as "webmaster mode, in-line editing, operate as a user popup". A lot of existing customers reports us that find this feature very useful, even who also migrates from v4 to v5.

You can fix your problem very easily: just replace the email for customer profile using + sing. For example, continue using "email@domain.com" for the admin account, but replace the email of the customer account with the "email+customer@domain.com" variant.