Folder/item-permissions and problem with DeleteChildren permission

Hello,

I'm using Alfresco Community 5.0.d.

I try to achieve the permission concept below in my document library.

For that I have created a new role "Moderator" in the files
alfresco-5.0.d/tomcat/shared/classes/alfresco/extension/model/permissionDefinitions.xml and
alfresco-5.0.d/tomcat/shared/classes/alfresco/extension/model/sitePermissionDefinitions.xml
and some other files.
The role is working (tested with different permission sets).

This is what I need to create:

• - Documents
  • - Folder A <- read permissions for all users for this folder and all children = working
    • - Folder A1 <- role Moderator must not delete this folder but must be able to create children (files and folder)
      • - Text-File A1.1 <- role Moderator must be able to delete this file, no matter who the author was (except owner = Admin / Site Manager)
      • - Folder A1a <- created by Administrator; must not be deleted by role Moderator
        • - all children <- role Moderator must be able to delete this files/folders, no matter who the author was (except owner = Admin / Site Manager)
  • - Folder B

So to clarify:
- I have 1 folder and 1 sub-folder created by Admin.
- role Moderator must be able to create and delete content in these 2 folders, no matter who the author was (except owner = Admin / Site Manager)
- Other sub-folders not created by an admin or Site Manager must be deletable by role Moderator.
- The specified 1 folder and the 1 sub-folder must not be deleted by role Moderator.

The problem I have is, that the permission "DeleteChildren" doesn't seem to work or only seems to work in combination with the permission "DeleteNode".
I can't give Folder A1 a permission (by setting the role Moderator), where sub-items can be deleted while Folder A1 cannot be deleted.

I found several other posts without a solution to the not working "DeleteChildren" permission.

Is this permission the wrong concept for what I try to achieve?
Is there any other way I can use to achieve the above concept?

Kind regards,
Joerg