not a bug
Weird bug
I guess that happens to everyone. Before or after a game, you can do whatever you want with the pieces.
Not a bug :)
Once the game ends, you the player are able to go back the the previous moves, and move both black and white pieces around the board. You can if you wanted, have one pawn take all other pieces and just leave one pawn remaining on the board. This is because the game is over and you're playing with the board on your own :) You can also do this with the initial board seen when entering live chess.
It won't affect the game history.
After I won a game, I looked back on the "move history," clicked the very first move, and then I'm able to move random pieces on the board around with no restriction.