I'm currently playing a character with fungal arts. Most of the time, when placing spore, I can click on any body or patch of dirt I can see, it doesn't matter if its at the far end of my visual sight range. But every once in a while, the game will suddenly decide that I can't place spore on any body I'm not adjacent to. Honestly, I'm not sure which is the intended behavior and which is the bug. When it decides to restrict sporing to adjacent squares, it does so for a random stretch of time, at least several minutes in length. It seems that if I level up, the game starts letting me place spore at any distance again. I don't think that's the only time it resets to unlimited range, though. I'm not certain, but I suspect there's some other factor to the reset because I don't think I've always leveled up. It may be that changing floors or saving the game is the culprit, or it may just be a matter of time or turns passed. I can't figure out what's causing it.
I would say it _doesn't_ limit me to adjacent squares approximately 80% of the time, sometimes for streaks of several hours before suddenly getting more restrictive for 5 to 20 minutes.