Advanced Wars by Web!

[Jolt]

It isn't a bug. >_> In foggy games, you can only attack targets you previously were seeing. If you happened by chance to move right to the next square that his tank stood on, you can't attack him. Only if you had, say a scout which was already showing the tank. Then you could move in and attack. Same goes for moving into or through a foggy square with a unit already on it. In that case, your unit will lose its turn and stand right next the square with the unit you intended to go. It's the "Ambush!" thingy.

[Chaotix]

Is that it? For some reason, I don't remember it being that way in the actual game... or perhaps it was that the fog didn't lift till after your unit "waited". In either case, it threw me off.