Land reluctant to change from decayed to bountiful

v 1.1

I think this is a bug, but it may not be.  When you capture a city from an empire opponent (you are kingdom), the land doesn't change to match the new holder.  I thought this might be a virtue of it being a fundamentally decayed city and that you'd have to cast some kind of spell to "heal" it, but I can't find said spell.  If I quit the game and restart it, the land automagically changes to its kingdom "healed" state.  That tells me something's not triggering correctly as it probably should be changing once a city changes hands or somethings not being explained sufficiently well.

I tried looking for explanations in the manual and in the forums but came up empty.

Thanks