Update: I've started to use the 'Paste LU v. ?HP' option to fill the lineups first, but there are still problems when I try to make minor changes.
If I want to make any small adjustments it will semi-frequently change one of the other lineups for the other 6-days by randomly placing the player I'm moving in the other lineup and deleting another player.
Have any of the developers had a chance to look into this? As someone who relies heavily on 7-day lineups it's making me slightly crazy.