Guess you already have plugins for the AddMember, AddListMembers messages. Had similar issue earlier when a message AddMembersByFetchXML was used to resolve it. This is not shown in the plugin registration tool and requires a database modification, which
is unsupported.
I guess when we select all the records from the AdvancedFind result set to be added to a marketing list, CRM treats it similar to adding members in a dynamic list.
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