Speaking of wandering, I've seen this guy like 50 tiles away from his wildland. I actually passed next to the wildland just as he agro'd onto an AI party, he chased them a couple tiles out, then started chasing my group for like 10 tiles, then I lost track of him. Few dozen turns later I ran into him in the middle of nowhere on the other side of the map.

I've experienced this too specifically with Vertrar. He is one adventurous fellow.

I"ve experienced a similar thing with Obsidian Golems from Imperia wildland, they just love to invade me when I'm using boar spears+Leather armor. In my current game progression I think i got hit by 7 of them but they all got killed anyways. Mainly because they was alone instead of in an army I would've been toast if they came at me in an army. Because 7 imprisons. However this makes invading Imperia a breeze because it will be empty of golems so my weaker armies can conquer imperia for me while my main ones protect me from AI factions.

Has anybody heard if this is going to be fixed?  I don't really want to play with this going on. 

Btw, I had a game where My capital was just 20 tiles away from Vetrar at beginning of the game. I held my breath and played. It wandered away from my lands and into Kraxis' lands and terrorized them. And it looked like it was going to keep on wandering away and away so I sent three armies towards Vetrar and kited him back into his wildlands. Took me about 30 turns but vetrar is back in the snowy wildlands where he stayed put until I got a ashwake dragon pet to bring him down very early in the game.

To kite, leave a weakling army just two tiles away from vetrar so that he will want to nom nom on the army of mcnuggets but keep it two tiles away, if Vetrar change his mind and go after something else, chase him until he chases you again then flee again and vice versa.

Rinse and repeat until vetrar is back in the wildlands where you can kill him to guarantee a wildland clear. Oh and don't get your army trapped by rivers, frozen rivers is uncrossable I noticed it just in time lol.

I tried kiting him back to his land once, it didn't work.  I got him to move maybe 3 squares then he decided he wanted to sit around there.  I gave it a few more turns and he wouldn't move.   I haven't played a game since, hope the next patch addresses this.  I don't know everything about the AI but I think what's missing in their AI wander code of the bosses is an if statement.   If the next step my algorithm has picked takes me out of my wildland don't go.  That's it.

I would not hold my breath. I reported this in beta (possibly the FE beta, been a while) with screen shots and even got a dev response telling us it wasn't supposed to happen, but it's obviously never been fixed. It's a long standing bug they have been aware of and likely don't have an easy way to fix so they just ignore it.

Not sure about that.  It never happened to me until after the last one or two patches.  I think they may have had it figured out at some point.  Hard to say.

I think it might be more the AI changes making the issue more common. AIs might be doing a better job moving around and exploring areas and being smart/aware enough to avoid these bosses when they get close rather than just blindly running into them and dieing. It was back in April ('13) that I last reported this, so not too long ago, and it was rare then and something I only saw a few times. I think the issue has always been that while these bosses are "leashed" to their wildland area, if you get them to chase you outside of the borders a few tiles that breaks the leash and they start to wander around the map. They might not have had much chance of chasing any AI stacks back then because the AI was so dumb and just walked right into them, making the issue more rare, but now the AI avoids being lunch and ends up dragging the bosses out a lot more. Or they fixed it while I wasn't playing and it broke again right before I came back.

 definitely it seems that they wander a whole lot more in the last patch 1.3 than the one before.

I would not complain about him wandering.  The problem is that the wildland is not opened when he gets killed.

N/A

Don't think anyone has mentioned this yet but, is the problem perhaps that you never entered his land to trigger the quest? If you just found him out wandering and slayed him without having the quest, that would seem likely to not let the quest finish.