Works for me.
Do you see the intended BCC address on the compose screen, before sending?
Can you try changing the identity to use its own outgoing mail server (tap the identity in the account's identity settings to change this) -- in case the outgoing mail server isn't happy about the BCC when sending via the "parent" account?
Finally, have you checked web mail in the identity's address, in case the BCC was sorted by the server into Spam?