I had my players move to a brand new map (so it had complete fog coverage) that has Night Vision selected. I had them all use the Map Explorer to find their tokens, then try to expose their vision. About 50% of them were unable to expose their vision.
I've seen this twice myself but haven't been able to recreate it intentionally.
In the first case it happened fairly early in the development of IV/IF and so I didn't worry about it much. Had 2 out of 5 players not able to expose. My actions also did nothing for them. In the second case it was just one player. Both times I had them disconnect and then reconnect. It worked for them after that.
Both cases were on maps that the tokens had never been to before. I cut/pasted the tokens to the new map.
Perhaps the Dev team needs to do as Dorpond suggested and have a "mock" game to try to figure out what the issues might be. I can't think of any reason off the top of my head why it would "break" for one map, but not another.
Phergus, perhaps you could take a look into the code. The way it works is that on a paste, it checks to see if the exposedAreaGUID is set on the token AND is not duplicated on the map already. If already on the map, a new exposedAreaGUID is created for that token. Then, any exposed area's area added to the zone in a map<GUID,ExposedAreaMeta> and this is checked for adding/removing any exposed area regardless of how.