Typically you have to move your units out of your opponent's territory once the War has ended, but my regiment of Saboteurs cannot seem to move at all. All tiles say "there is no viable path to this location". It does let me click to move and attack on one of my opponent's unit's, at the cost of starting a surprise war. 

My theory of this is that whatever enables your units to move out of the opponent's territory post war is not applied to the stealth units (as the "opponent's camera" cannot see them)  rendering them immobile other than queuing an attack, as they cannot "enter" an opponent's territory in peacetimes. Notably, they do not take damage per turn or trigger trespassing.

If I get my opponent to give me open borders, the unit can move freely again.

I've provided a couple screenshots to show the problem.