I found some additional information: debugging sql queries performed by
LiveCycle apis, I found that TaskManagerQueryService.processSearch(...)
always applies a filter to check if the user used to perform the search,
has performed at least a task for an instance (it apply an sql filter on
tb_queue.workflow_user_id joining it on tb_assignment, tb_task and
tb_process_instance), even if this behavior isn't documented on javadoc.
This means that, in contrast with workspace that starts a process usin...