From Lotus Notes the multiple forward of two or more Enterprise Vault archived items does not always work properly.
The newly created memo does not include all the items supposed to be forwarded.
The multiple forward action is not including in the newly created message the items which contain the attribute $REF (this indicates that the item is a 'response', the $REF field contains the UNID of the parent document).
This issue has been addressed in the following release:
Enterprise Vault 10.0.4 Cumulative Hotfix 3 Release
Enterprise Vault 11.0 0 Release Details