Takayuki, this looks like a mistake on my part. There is nothing wrong with the plugin. What happened is I removed the "WP-Mail-SMTP" plugin and tried to implement its functionality within functions.php.
I had implemented the "wp_mail_from" WordPress hook to set the "From" address, but I had not realized it would override Contact Form 7's setting of the From address.
I need to find a workaround to this, as the WP-Mail-SMTP plugin is problematic, but Contact Form 7 is solid.
Thanks for looking into this false report.