yeah this is a pretty big bug.    It's been going on at least a year apparently: https://forums.stardock.com/426899/page/1/  and I reported it again a couple days ago: https://forums.elementalgame.com/448233/page/1/#3395891 in the LH Support forum.

I haven't seen any official word from Stardock that they plan to address this. 

I hope so, because the current game is pretty much ruined if you get his wildland.  Once he starts leaving his area he's going to attack your cities (not the AIs) and if you manage to kill him, his lands are still going to be wildlands - they don't turn fertile like they are supposed to.

Thanks for the info.