I have also noticed some issues with BCC:
if there is an email in the bcc list that is not valid ( e.g. a name instead of email address) which is acceptable since there is no regular expression check on email addresses when signing up the whole BCC operation fails. Once the invalid address is corrected i can send with the BCC option.
As for Asynchronous it doesn't seem to work at all these are both really irritating issues so i hope someone here will respond to this.