user registration cannot be completed if a user with the same email prefix exists
Version 3.5.4 released the Auto-population of username with email prefix(all chars preceeding '@' sign)
feature. While this is a useful feature, it is now impossible for users with the same email prefix to register. For example, if jonathan@company1.com
exists in the system, then jonathan@company2.com
will not be able to register, because he will receive a "Username exists" error.