Using 1.4.7 support build - Zenpage Theme. Found the following problem:
Users with different Users ID but with same email address can both register. e.g.
If there is already a user who has registered with a user id of "user1" and an email of "user1@testmail.com" then a second user can register with a user id of "user2" and the same email as user1 i.e. "user1@testmail.com"
However if the second user also uses the same user id e.g. user1 then the "Registration Failed" Message comes up saying that user ID user1@testmail.com is already in use.
Moreover if the second user uses the same user id i.e. user1 but a different email address e.g. user2@testmail.com then the "Registration Failed" Message comes up saying that user ID user2@testmail.com is already in use which actually is not the case. It should give the message that user ID is already in use.