All emails (excerpt user registration) related to forum are being sent from the EMail you configured in the Forums > Settings > Emails admin page. User registration process is under WordPress control, not wpForo. wpForo only provides with registration form, other processes are performed by WordPress. And yes, this is a known issue of WordPress. This is the default Wordpress email. You should change it using some hooks like this:

add_filter( 'wp_mail_from', function( $name ) {return 'info@mydomain.com' ; } ) ;
add_filter( 'wp_mail_from_name', function( $name ) {return 'My Forum name' ; } ) ;

Change the red marked strings and put this code in your current active theme functions.php file. Make sure you didn't deleted the apostrophe before and after the strings.

More info about this issue: http://www.wpbeginner.com/plugins/how-to-change-sender-name-in-outgoing-wordpress-email/