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Hi,
If you have in the source drawing file multileader with the same style name as in target drawing (in fact multileader properties can be essentially different) and you paste multileader from the source drawing to target drawing it will take all the properties from multileader in target drawing.
You need at first to rename multileader style in one of the drawings, than you will have two multileader styles in target drawing after you paste multileader from source drawing.
Maxim