at the moment when I duplicate a track on the new track the shared instrument parts are lost.
But as they are exactly the same parts why shouldnt they be shared.
Same happens when copying to/from Scratchpad FR here: https://answers.presonus.com/26835/copying-scratchpad-instument-separate-scratch-shared-copies
Also it would be great to select all instrument parts that contain the same notes and make them shared. This could be a good workaround for this problem and could solve other situations. (FR for this here: https://answers.presonus.com/20605/select-instument-parts-contain-shared-copies-choose-color )