create a long movement path
execute the move
in the middle of the move (while the unit is moving), click on the unselect army button
the army will stop moving (will not finish the executed move)
Now try to reselect the army. one of two things happens
1. you get an out of snyc error
2. you cannot select any unit by clicking on it
you can select a different army by using the next army unit button, but you can't get back to your original unit without reloading the game