Ok, the "hi" portion is normal. When sending via BCC it sending one email to multiple users, so it can't include the username.
As for the email problem. Since it's taking the first letter of the email address, it seems to be treating the array as a string. I'd guess maybe there is a mismatched script somewhere.
First thing I'd do is double check that you upgraded everyting, specifically all of the files in the libs directory.
