All of our games that feature player selectable people (whether villagers or family members) will, by default, accept the currently displayed selection if the game is closed while the selection screen is open. That's normal. It seems that your game is not having enough time to save that rejection before you close the game, so the game acts as if the selection screen is still open.

To avoid this, reject the proposal, play for a few minutes to allow the game to save after that rejection, then close the game.

The game should automatically save your progress every two minutes.