Selecting multiple existing linked layers and duplicating (via Layer/Duplicate Linked menu item) only "duplicates link" one of the selected layers, while other selected ones are duplicated unlinked.
At least this happens in Photo, to pixel layers, that's what I had trouble with.
I can select an individual curve and choose "Layer -> Duplicate Linked" to create a copy where changes to the original will be applied to the copy.
Is there any way to do this for more than one curve at once? If I try selecting more than one curve then "Duplicate Linked" is still available in the menu, but if I click it only the first object is duplicated linked; the remaining objects are duplicated in the ordinary way, i.e. not linked.