Dynamic light doesn't always work

I tried to run a game where there was a fight in a dark open cavern, but all the players did not need lights, they could see everything on the map. It turned out it was because one player had improved (120 foot) nightvision... when this player was on the map all players could see the entire cavern. This seems broken to me. There is no reason a player without nightvision should be able to see through the eyes of the drow who had nightvision: he should be blundering around in the dark. As a workaround I turned off dynamic lighting on the Drow's turn, and turned it on for everyone else.

This was almost certainly due to an improperly set setting. Darkvision is not seen by other players if done correctly. Assuming this is legacy, the darkvision character should be given sight, made to emit light (I would suggest the settings -5 and 120), and "Others see light" should be clicked off. This will give them "light" that only they can see. Also, make sure that everyone controls only their own character. Shared characters share vision and light. If this was set up in Updated Dynamic Lighting, I would suggest not depending on that for a game. It's an in-development feature.