I set a Parent project for my project and some sprints and backlogs for parent project (in OpenERP v6) 1- Why I can not use Sprints defined for parent in the sub-project? 2- Why I can not use Backlogs of the parent project in the extsting sub-project's tasks?

Example: I define ParentProject1 and SubProject1 and I assign ParentProject1 as parent of SubProject1. 1- I define a "Sprint1" sprint for ParentProject1. Now I want to define a backlog for Sub Project1 and assign Sprint1 to it. But I can't. 2- I define "Backlog1" backlog for ParentProject1, I also define Task1 in SubProject1. Now I want to assign Backlog1 for Taks1. But I can't.