In file kernel\classes\confirmorderhandlers\ezdefaultconfirmorderhandler.php we have double mail sending code from line 87-98

$emailSender = $ini->variable( "MailSettings", "AdminEmail" );

if ( $tpl->hasVariable( 'content_type' ) )
$mail->setContentType( $tpl->variable( 'content_type' ) );

$mail->setReceiver( $email );
$mail->setSender( $emailSender );
$mail->setSubject( $subject );
$mail->setBody( $templateResult );
$mailResult = eZMailTransport::send( $mail );
@@---
$email = $ini->variable( 'MailSettings', 'AdminEmail' );

$mail = new eZMail();

if ( $tpl->hasVariable( 'content_type' ) )
$mail->setContentType( $tpl->variable( 'content_type' ) );

$mail->setReceiver( $email );
$mail->setSender( $emailSender );
$mail->setSubject( $subject );
$mail->setBody( $templateResult );
$mailResult = eZMailTransport::send( $mail );@@

Steps to reproduce

After you purchase item admin is receving two mails.