Shared MIDI parts locked

I have two instrument tracks, and for some reasone all of the midi parts on the first one are copied to the second track, they appear to be shared with the ones on the first track, judging on the little icon in each part’s right upper corner. If I select a part on the first track, Nuendo also selects the shared part on the second track, so I cannot convert to real copy. How can I get rid of those parts in the second track?