It's happened to me twice now and I think it should be something that the developers could look at that would improve the game.
Ive been in a coalition or working with a partner and we have exchanged right of way.
Works well for a few days as you team up against someone or another coalition and then suddenly with all your troops engaged or out of the way the other player declares war on you and their troops stationed in your provinces take them all in seconds and you cant recover.
Is there anyway that developers can put a time lock on this similar to joining and leaving a coalition where if a player has right of way and then cancels it they can attack the player for x amount of hours?
Otherwise the trust element and teamwork is ruined while this tactic is allowed to continue.