How does pre-move get turned on! I have not consciously turned that on and then a message says click anywhere to cancel. I have lost pieces when that happens.
This happens when you click and drag a piece during your opponent's turn. For example, If you have just opened 1. e4 and, before your opponent moves, click and drag your pawn to d4, you will have made a 'premove' to that spot. If the move is still legal after your opponent's move, you will automatically make that move.