Yes, I know that is the case but I had confimed seats in premium economy since March this year which I selected on LH.com when I made the booking.

If I log into lh.com now and go to my booking I can open up the seat plan and it lets me select seats in the premium economy section and shows them as "preferred" - my experience is that a seat will be blocked out and not selectable if I am not able to take that seat.

I would never have tried to move the seats if I knew the system would deny the change and leave me with no seats allocated.