[Plugin: WP Document Revisions] Not private by default

Hi,
I want to undo the make_private by default part of the plugin.
There is a filter document_to_private that should enable this. It passes $post and $post_pre to the filter.
My filter looks like this:

add_filter( 'document_to_private', 'dont_make_private', 10, 2);
function dont_make_private($post, $post_pre ){
	return $post_pre;
}

This doesn’t work.
die($post->post_status); and die($post_pre->post_status); both result in private.
My PHP version is 5.3.2-1ubuntu4.17 (?).
Is that a bug?
Thank you

Marvin

http://ww.wp.xz.cn/extend/plugins/wp-document-revisions/