Not a bug, there's a reason for this exception:
Building a fire needs to be allowed even if you don't see the tile. That's because otherwise you couldn't build a fire the pitch-dark winter night because of "select the direction you can see".
It feel funny to do it behind your back, but surely a master woodsman can do that also
![Wink ;)](https://www.unrealworld.fi/forums/Smileys/default/wink.gif)