Activity to business process as a component

What rules am I breaking if I link the same activity object to more than one business process object on different process models? I generate two seperate workflow models, which has this one activity object in common.  I did it to facilitate re-use. If I generate a report using the publication option the numbering of the objects in the underling workflow model is not the same as the number on the model (What I see) in PV?

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