[Exim] malformed recipients vs. set sender

If I send a message to (for example) jp@dalbec@??? using IMP, the
recipient address is changed to
jp@dalbec,UNEXPECTED_DATA_AFTER_ADDRESS@.SYNTAX-ERROR.
Exim produces 3 error messages. One for the delivery failure of jp@dalbec, and
two for the malformed recipient address. However, only one of the "mailformed
recipient address" messages is returned to the set sender of the message. The
other two errors are sent to the web server user. Is this a bug?
John