Shared mail: some kind of mail are not delivered

After implementing shared mail (with option transfer and delivery and shared_mail=2) we notice that same mail are not routed (they remain in mail1.box or mail2.box).We noticed that these mail are mail with copy/paste attachments (e.g a copy paste from excel or paint)

While mail created with insert attachment works correcty.

Domino release 6.5.4.

Thanks in advance for your suggestions.

Piero Milana