I remember playing Stratego as a kid at a friends house, and eventually found out some of his pieces were subtly marked (chip in the pieces). Unhiding information was very unfair :)
In real life this leads into the wonderful arena of deception: I create an information side channel, which you detect and begin to rely on, thinking it is secret, but I can then lie about.
Common issue with this game. The red bomb in mine had been stepped on, at which point it became too conspicuous.