In my current game, there appear to be some Sovereigns that got cut off from their kingdom. They have been stranded for some time.

The first one, the stuck Sovereign is just to the right and up a bit from the city in the middle. His kingdom is towards the bottom of the screen. He just sits at the border there. He has been there since very early in the game. Apparently he went exploring and I built a settlement which later blocked him from getting home.

http://img842.imageshack.us/img842/4048/strandedsov1.jpg

In this one, the Sovereign is to the left of the center city, looking like he is intent on going for the bandit nearby. Both the bandit and that Sovereign have been there for several turns without moving.

http://img507.imageshack.us/img507/9627/strandedsov2.jpg

In this shot, there are some enemy units that were apparently close to the city when I took it, but they are now stuck there and I can't attack them either, even tho it gives me the crossed swords symbol.

http://img840.imageshack.us/img840/5557/strandtrader1.jpg