cj20n milestone attachment file does not work

Hello,
When we create attachment files for Milestone, they are linked to network (BUS2002) and not to milestone (MLST_NETW), as expected.

Example : CJ20N

       Network – 1000 - N1
                  Activity 01 - A1
                        Milestone A :

                               Attachment file X
                        Milestone B         
                               Attachment file Y.
Actually, in the Network, Activity and Milestones all files created under the Network 1000 are displayed.

We create an attachment file with right click on Milestone A :  Services For Object -> Create -> Create ATTACHMENT

Our customer would like to see attachment file X and Y only into there respective Milestone A and B

BUT he doesn't want to see the same attachment files on A1 and N1.

In OAC3 , we added object type MLST_NETW with doc type BDS_ATTACH, but unfortunately, this entry has no effect.
Do you see any solution to resolve this problem ?
Thanks for your help,

Message was edited by: GLT GLT