clearbeard
King
I've got one with mana nodes and building a city. I build a Law Mana node in my territory, and when sending a settler out to expand and reinforce my cultural borders, I noticed that I was able to actually build the city right on top of that node. When I built the city, I still had access to the mana itself. Nice little way to protect your mana lol
Trouble with that is, as far as I know, you can never change that law mana to anything else. So make sure you don't settle on a raw mana node!

[edit:] Hence, I don't think it's a bug, just a choice you have to make for yourself. There was one related to the AI settling on raw mana nodes, but I think that's been fixed.