It'll help if you post screenshots and give more information about your game setup, such as whether you're using Updated Dynamic Lighting or Legacy Dynamic Lighting, what settings you have on tokens, etc. If you are using Updated Dynamic Lighting, the likely answer is that it is a bug. That lighting system is basically a live beta test. Otherwise, it sounds like you may have incorrectly set your tokens so that all players are able to control each other's tokens, which would give them shared vision.