Copy paste keeps link information

e146aba2e5

1. Create a score with 2 linked staves
2. Add 4 quarters in the first measure
3. Select first measure and copy
4. Paste in measure 2 and 3
5. Change the pitch of one of the notes in measure 2 --> measure 3 changes as well ! m2 and m3 are linked.
6. Something more : Save and reload, change a pitch in measure 1, measure 2 and 3 change as well.

Critical : potential lost of data.