<?php if ( $checked_status ) echo 'checked="checked" '; ?>
in your main gurken-subscribe-to-comments.php
is clearly meant to query if an option was set in the settings as to whether to check the checkbox by default, but it does nothing, as there is no option in the settings page. Thus, I removed the above code and replaced it with
to achieve my desired result.
Might want to fix that in your next update.