I was able to reproduce it, thanks a lot for reporting it. I will create a ticket in our bug-tracking system so this can be fixed as soon as possible.
As a workaround, I've been able to fix it by modifying the
$pageroot variable in the
/opt/bitnami/apps/phplist/htdocs/config/config.php config file, from
/ to an empty string:
$pageroot = '';
In any case, please note this is just a warning and shouldn't affect the normal operation of the application.
We will let you know once a new release containing a fix is released.