The following documentation pages list the "all_relations" parameter as a boolean. This is not correct.

http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Reference/Modules/content/Fetch-functions/reverse_related_objects
http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Reference/Modules/content/Fetch-functions/related_objects_count
http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Reference/Modules/content/Fetch-functions/reverse_related_objects_count

The related objects documentation page is correct:
http://doc.ez.no/eZ-Publish/Technical-manual/4.x/Reference/Modules/content/Fetch-functions/related_objects

For more information, see: http://share.ez.no/forums/developer/reverse_related_objects_count-improvement-how