Creating New User Account in Admin Allows Existing Email Address Without Warning

[thekenshow]

There is no warning when creating accounts that the email address provided already belongs to an existing user.

1. I created a new account with a new and unique username, but used an email belonging to an existing account.
2. I expected the Admin would warn me that the email address is already in use.
3. The Admin went ahead without any warning and created a new account with an existing new email address (one that belongs to another account).